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.

This involves redesign of the web recording dialog in order to look the
same as the mobile one.

There were getDomain, setDomain, SET_DOMAIN, setRoomURL, SET_ROOM_URL
which together were repeating one and the same information and in the
case of the 'room URL' abstraction was not 100% accurate because it
would exist even when there was no room. Replace them all with a
'location URL' abstraction which exists with or without a room.

Then the 'room URL' abstraction was not used in (mobile) feature
share-room. Use the 'location URL' there now.

Finally, removes source code duplication in supporting the Web
application context root.

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.