Up until now we relied on implicit loading of middlewares and reducers, through
having imports in each feature's index.js.

This leads to many complex import cycles which result in (sometimes) hard to fix
bugs in addition to (often) breaking mobile because a web-only feature gets
imported on mobile too, thanks to the implicit loading.

This PR changes that to make the process explicit. Both middlewares and reducers
are imported in a single place, the app entrypoint. They have been divided into
3 categories: any, web and native, which represent each of the platforms
  respectively.

Ideally no feature should have an index.js exporting actions, action types and
components, but that's a larger ordeal, so this is just the first step in
getting there. In order to both set example and avoid large cycles the app
feature has been refactored to not have an idex.js itself.

* Fix chrome extension banner

* Address reviews

- Remove network-activity "feature"
    - It wasn't in use
    - It relied on internal React Native components, bound to break anytime
- Show an infinite loading indicator
- Style it just like the LoadConfigOverlay
    - Since it kinda represents the opposite, an "unload" then SDK is done

Fixes: #312

It need not always exist, since it's created asynchronousluy on app
initiualization. Make sure we are ready for it.

I've seen backtraces because of this.

* fix(invite): decode the meeting name

* squash: try to make mobile join same encoded meeting name as web

* Decodes and generated texts for share and copy meeting info.

Decodes in all cases except when it contains a space, as it will generate wrong links when pasted/shared in external applications.

The only way to render the welcome page in reduced UI mode currently is to
hangup a call from the Android ongoing notification while in PiP mode.

In case wrong props are passed in, such as pointing to
an index that does not contain a value in the tabs
array.

This reverts commit 890151fa72.

By making the container 100% height and position relative, that
would cause it to overlap any static-positioned  elements below it.
The 100% makes it so that any watermarks intended for the bottom
of the page show up on the bottom of the page. However, it's not
needed because watermark stylings already try to position the
watermarks at the bottom.

🔥🔥🔥

This new version comes with an updated JSC runtime, so we no longer need to
depend on the updated version ourselves.

Remove caching of calculated styles, thereby removing
componentWillReceiveProps, by passing in base styles
and passed in styles when rendering.

To kill componentWillMount, call destroyLocalTrack after mount.
Navigation to the blank page was synthetically forced and no
UI issues were noticed, possibly because destroyLocalTrack may
already be async so destruction may already have been occurring
after mount.

For the most part the changes are taking the "static propTypes" declaration off
of components and declaring them as Flow types. Sometimes to support flow some
method signatures had to be added. There are some exceptions in which more had
to be done to tame the beast:
- AbstractVideoTrack: put in additional truthy checks for videoTrack.
- Video: add truthy checks for the _videoElement ref.
- shouldRenderVideoTrack function: Some component could pass null for the
  videoTrack argument and Flow wanted that called out explicitly.
- DisplayName: Add a truthy check for the input ref before acting on it.
- NumbersList: Move array checks inline for Flow to comprehend array methods
  could be called. Add type checks in the Object.entries loop as the value is
  assumed to be a mixed type by Flow.
- AbstractToolbarButton: add additional truthy check for passed in type.

* feat(welcome-page): Redesign.

* Style adjustments.