* Removes unused config logic.

* Whitelists config options that can be overridden using the URL.

* Recorder login with credentials, not supported by externalconnect.

Jibri uses xmpp credentials to login, which is not supported by externalconnect, so we want to skip it till that is supported.

* Whitelist only config.js

* Extracts whitelisting in separate function.

* 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.

Iterate over objects and copy over primitives and arrays
instead of using _.merge, as merge will not replace a config
entry completely. For arrays in a target object, the arrays
will have its indices replaced. This means if a source array
is empty, the target array will be left alone. Similarly,
if the target array is longer than a source array, there
will be indices not touched in the target array.

This makes it possible for the following URL params to work:

config.p2p.enabled=true&config.p2p.preferH264=true

Make 'Add jwt module to react' work on mobile.