Web's ExternalAPI accepts an object with properties as one of its
constructor arguments and from which it generated a URL. Mobile's
JitsiMeetView.loadURLObject is supposed to accept pretty much the same
object.

Introduces loadURLObject in JitsiMeetView on Android and iOS which
accepts a Bundle and NSDictionary, respectively, similar in structure to
the JS object accepted by the constructor of Web's ExternalAPI. At this
time, only the property url of the bundle/dictionary is supported.
However, it allows the public API of loadURLObject to be consumed. The
property url will be made optional in the future and other properties
will be supported from which a URL will be constructed.

Also expose this in the native SDKs.

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.

`host` contains the hostname:port portion, whereas `hostname` is just the
hostname, not including the port.

A bug was discovered in d17cc9fa which would raise a failure to push
into the browser's history if a base href was defined. Fix the failure
by removing react-router. Anyway, the usage of react-router was
incorrect because the app must hit the server infrastructure when it
enters a room because the server will choose the very app version then.

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.