Adds base/sounds feature which allows other features to register a sound
source under specified id. A new SoundsCollection component will then
render corresponding HTMLAudioElement for each such sound. Once "setRef"
callback is called by the HTMLAudioElement, this element will be added
to the Redux store. When that happens sound can be played through the
new 'playSound' action which will call play() method on the stored
HTMLAudioElement instance.

Recently/as part of the work on taking into account the user defined by
JWT, the local participant (on mobile) started telling the remote
participants that he/she had the display name "me". Obviously, that's
incorrect. Do not store the default display name in redux. While it may
be argues that redux is the place for all states, base/participants and
the name property of Participant is not meant to be that display name
because that is being sent to remote participants, the default name
needs to be internationalized, etc. So it's better to not store the
default display name at this time at all because it's not used by mobile
anyway and Web already deals with remote participants who don't share
their display names.

Will override email, display name and avatar URL with the values
provided in 'context.user' structure of the JWT token.

Settings will no longer be used to retrieve local display name,
email and avatar URL. Now those values will be obtained from
the /features/base/participants Redux state.

fix(jwt/middleware): use const for default name

fix: wrong default display name on web

ref(base/participants): remove getDisplayName functions

ref(jwt): do not accept unknown user fields

* Javadoc introduced @code as a replacement of <code> and <tt> which is
  better aligned with other javadoc tags such as @link. Use it in the
  Java source code. If we switch to Kotlin, then we'll definitely use
  Markdown.

* There are more uses of @code in the JavaScript source code than <tt>
  so use @code for the sake of consistency. Eventually, I'd rather we
  switch to Markdown because it's easier on my eyes.

* Xcode is plain confused by @code and @link. The Internet says that
  Xcode supports the backquote character to denote the beginning and end
  of a string of characters which should be formatted for display as
  code but it doesn't work for me. <tt> is not rendered at all. So use
  the backquote which is rendered itself. Hopefully, if we switch to
  Markdown, then it'll be common between JavaScript and Objective-C
  source code.

* feat(display-name): convert to React

- Create a new React Component for displaying and updating display
  names on small videos
- The updating of the Component is defined in the parent class
  SmallVideo, which children will get access to through prototype
  copying
- Create a new actionType and middleware so name changes that occur
  in DisplayName can be propogated to outside redux
- Update the local video's DisplayName when a conference is joined
  or else the component may keep an undefined user id

* squash: query for the container, not the el owned by react

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.