config: Don't require an extension for firefox >=52.

Starting with firefox 52, no extension is required for screensharing.
See https://wiki.mozilla.org/Screensharing

cleanup: remove old adaptive simulcast config option

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

fix(filmstriponly): Set the background to transparent

Volume slider for remote participant audio elements

Recent versions of the Android plugin for Gradle started to automatically
download the SDK build tools dependency if it is not installed already.
So it is no longer necessary to have the developer of the Android app
install the SDK build tools dependency in advance.

Move miscellaneous files to resources

Re-styles range inputs for Chrome and FF.

When rendering using a for loop each child whould have a key prop.

This solves the issue of view clipping on Android, plus it seems to be the RN
convention unless the views are very large and memory hungry.

doc: fix markdown link syntax in mobile docs

Fixes an issue where immersive mode would be enabled when coming back from the
background on the welcome screen.

Re-fixes c57e713, which was not correct.

It doesn't work properly and gives a very bad user experience. Disble it until
all underlying issues in react-native-webrtc are ironed out.

On RN we don't use the global APP object, so don't save the store there unless
it's defined, which is the case in the current web version. Also, check for
undefined explicitly, since a "if (!APP)" check will throw a ReferenceError.

The mobile app remembers the domain which hosted the last conference. If
the user specified a full URL first and specified a room name only the
second time, it was not obvious that the second conference would be
hosted on the domain of the first conference.

doc: document resolution config option and set it to 720 by default

Now that Apple have approved build 1.2.199 for release in the App Store,
the short app version needs to be incremented; otherwise, no new builds
can be uploaded to TestFlight and, respectively, for release in the App
Store.

Fixes manual triggered tooltips text and no hover.

cleanup: remove adaptive las N config option

The feature has been replaced so the option no longer applies.