Introduction of account API

Provides method to retrieve balance, and some first drafts of conference-
related methods.
Enable DTLS for conference calls
Stop auth managers restarting after stop request
Added conferencing features to media API
Made invite return null as described in jsdoc
Attempt reauth on 403 errors to REST requests
Added rest call to list conferences
Additional conference management methods
Added support for constraining bandwidth
Fixed array traversal when inviting participants
Allow conference layout to be specified
Merge branch 'master' into conference

Conflicts:
	src/Media.js
	src/MediaSession.js
Merge branch 'master' into conference