Adds 1 liner notifications to mobile. Only the title is displayed. In
case the title is missing there's a fallback to the description.

- add 10px of padding on the sizes of the toolbar
- make the button margin smaller (from 10 to 7)
- increate the secondary button factor to 85%, thus rising the maximum secondary
  button size to 50 (from the previous 48)

It's designed to cover a container and give it a "tint" by using a color and
opacity.

With the introduction of wide and narrow layouts the margins of the
Filmstrip and the Toolbox became inconsistent. For example, the
Filmstrip's top in the wide layout was nearer to the top than the
secondary Toolbar.

Adds the ability to detect app area's aspect ratio on react-native
through the features/base/aspect-ratio.

Makes conference, filmstrip and toolbox react to the aspect ratio
changes and display filmstrip on the shorter side of the screen.

The files styles.js are used (pretty much) on React Native only and each
of them exports 1 name. Export it as default to cut down on source code.

Looks like Android gets confused as to what surface to blit when we hide or
show toolbars. Setting a border on the container, seems to force the entire
area to blit properly.

Other attempted approaches, with no success:
- zIndex of -100
- width and height of 0
- opacity of 0 and setting 'disabled' on touch containers

This patch applies the workaround in the welcome page and conference containers.

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.