misc: drop dependency on prop-types and polyfill

deps: update webpack loaders

ref(hangup): clean up some UI state on hangup

ref(app): move url change handling to componentDidUpdate

We no longer need it since Rect 16 takes care of passing the context around.
It's also deprecated: https://atlaskit.atlassian.com/packages/core/layer-manager

- bump expose-loader to 0.7.5
- remove unused file-loader

NOTE: The first incarnation of this commmit also removed string-replace-loader,
but alas lib-jitsi-meet lists it as a devDependency so it's not installed and we
are currently running webpack on install. This is arguably wrong, but that's a
discussion for another day.

Instead of handling the side effect of navigating to another
url from within componentWillReceiveProps, try to match the
same logic instead in componentDidUpdate.

Also update the bundle ID since we don't release with that anyway.

Touch feedback manifests in some ugly black border bleeding out of the thumbnail
itself. Since we already provide feedback (be that by adding the blue border in
case of pinning, or showing the menu in case of long press) the perception is
the same, without the graphical glitch.

- Change the existing overrides to move the flags
  so the first flag does not cover the toolbar.
- Add a new override to disable the slide in
  animation, as it will play for each flag once
  it becomes the first flag--instead of playing
  only once when the flag queue has items.

A CSS override prevents atlaskit theme from setting a
dark background on the top toolbar. With the upgrade
of the theme package the CSS class names changed.

- Reset some state on the singletons conference
  and VideoLayout.
- Add a way for LocalVideo to clean itself up
  by sharing logic with the other SmallVideos.
- Add clearing of chat messages so they don't
  linger.
- Remove some UI event listeners.

componentWillMount is a deprecated lifecycle method;
componentDidMount should be used to kick off things
like ajax. In the case of the _App hierarchy, a promise
chain is used to perform initialization, and it is
first started in the constructor by initializing
storage. However, by the time storage is initialized,
resolving the first promise, _App has already mounted.
So, move it all to the componentDidMount lifecycle.

ref(welcome-page): remove unused atlaskit overrides

WelcomePage used to use @atlaskit/tabs to switch between
recent meetings and calendar meetings. @atlaskit/tabs is
no longer used there so remove the css hacks which made
it look more presentable.

* Fix LoginDialog hidden by gUM-Overlay

Running FF46 on Linux and Android. The gUM Dialog (zIndex 1013) hides the LoginDialog (zIndex 999 by default) , but the gUM Dialog will only be resolved when connection is completed (aka hideUserMediaPermissionsGuidanceOverlay is called once the Promise.all in createInitialLocalTracksAndConnect is resolved and that Promise includes "connect").

Fix this by increasing the connection dialog zIndex.

Alternatively this could by fixed by handling gUM and connection one after the other.

* remove whitespace change

chore(dep): bump @atlaskit/modal-dialog 6.0.12 to 7.1.2

Adds the component which receives the messages from client and a module which enabled on a virtual host will start advertising the component. When clients discover the component they will send message to the component with the name of the room where the dominant speaker event happen.

The package now requires using a ModalTransition component
to handle animations. The existing DialogContainer component
has been split into native and web implementations to support
this change.

Apple rejected our app on account of requiring Dropbox not being acceptable. Oh
well! Disable it until we find a way around it. Sigh.

The avid reader may notice we have switched to using our own fork. That is
indeed the case. The upstream author hasn't maintained the library in months,
and changes to the Android build system are required at this point, hence the
fork.

It's possible for the YouTube api to return zero broadcasts
or broadcasts without any streams--streams are what are
associated with stream keys. In this case, instead of showing
an empty selector or no selector, show a message with a link
to where the stream key can be obtained.

Add some live stream key validation

On tile view enter/exit, local video is moved in the DOM (an effect
of not being reactified and moving being easier) and play is called
on its video element. The race condition setup is such: in tile
view with other participants and local video is on large (not
visible in the UI but visible in the app state and pip popout).
The race is such: pin a remote video, large video update is queued,
tile view is exited, local video is moved, play is called,,
onVideoPlaying callback executed, middleware fires mute update,
which checks if local is on large (it is), previous large video
update is cleared, and local is placed on large.

The fix is ensuring the redux representation of local video is
passed in, which holds the boolean videoStarted, which prevents
the onVideoPlaying callback from firing on subsequent plays.

Note that Android 9 Pie (API 28) disallows HTTP requests by default, so an
exception was needed in the app in order for the Metro bundler to work in debug
mode.

The Google repository is already added with google().