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.

Contributing all buttons in one place goes against the designs that we
set out at the beginning of the project's rewrite and that multiple of
us have been following since then.

The inline classes for the toolbars were re-arranged
to fix non-rounded corners in the always-on-top window's
toolbar. However, those classes were also used by the
torture tests as a way to find stable elements that will
not get blown away by a react re-render. So re-wrap the
buttons with a div that will not get blown away,
add back the inline classes to those divs, and change
the CSS to round the corners in the always-on-top
window's toolbar.

Rounded corners on the first and last buttons. Size of the hangup button
on hover.

The popovers in filmstrip only are displaying thinly.
As a quick workaround, set a width on them. There
should only be one anyway, which shows up when
talking while muted.

* ref(info): be able to open dialog through store

* feat(info): automatically show the info dialog

Conditions:
- Lonely call
- Has not opened the info dialog yet

* squash: change to show on start, hide later

* squash: update naming and comment

Prepare for React 16.

The torture tests were looking for the anchor tag within each
button. However, that anchor could get blown away from a react
re-render. So instead, expose a way for the torture tests
to find the root node of the button.

config.disableDesktopSharing - when set to false will disable desktop
sharing

interfaceConfig.DESKTOP_SHARING_BUTTON_DISABLED_TOOLTIP - when value is
assigned, will not hide the desktop sharing button completely, but show
as disabled with this value used as the tooltip text.

Audio only mode can be used to save bandwidth. In this mode local video is muted
and last N is set to 0, thus disabling all remote video.

When this mode is enabled avatars are shown.

As a step toward merging jitsi-meet-react with jitsi-meet to share as
much source code as possible between mobile and Web, merge the part of
jitsi-meet-react's source tree which supports mobile inside the
jitsi-meet source tree and leave jitsi-meet-react's Web support in the
source code revision history but don't have it in master anymore because
it's different from jitsi-meet's Web support. In other words, the two
projects are mechanically merged at the file level and don't really
share source code between mobile and Web.

As an intermediate step on the path to merging jitsi-meet and
jitsi-meet-react, import the whole source code of jitsi-meet-react as it
stands at
2f23d98424
i.e. the lastest master at the time of this import. No modifications are
applied to the imported source code in order to preserve a complete
snapshot of it in the repository of jitsi-meet and, thus, facilitate
comparison later on. Consequently, the source code of jitsi-meet and/or
jitsi-meet-react may not work. For example, jitsi-meet's jshint may be
unable to parse jitsi-meet-react's source code.