Rename setStateProperties and setStateProperty to assign and set,
respectively. Inspired by Object.assign, _.assign, and _.set.

They better represent if a participant has video available or not. There are
cases when even a participant in the last N set would not have video because it
disconnected momentarily, for example.

Replaces changeAvatarID, changeAvatarURL and changeEmail with
participantUpdated action.
participantUpdated can be fired for local user without id. This
fixes the problem with updating the local user before the user
join the conference which results in fix for failing to execute
commands for avatarID, avatarURL and email right after the iframe
api creates the iframe with Jitsi Meet.

Until we make a decision on access modifier hints and adopt a respective
coding style, consistency is king.

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.