Archive events.xml file in a concurrency-friendly way.

With the current segment processing, we might be processing one segment
while archiving a different segment from the same recording. To avoid
that the processing scripts see an incomplete events.xml file, write to
a temp file then rename.

Workaround video sync issue due to red5 timestamp offset

Red5 sometimes writes webcam video files with a large offset in the
video frame offsets, sometimes up to 30 or even 60 seconds. However,
the start event in the events.xml file corresponds to the time at
which red5 received the first keyframe (recorded frame) in the video.

The end result is that the video will sometimes appear to be
delayed (out of sync) in the processed recording.

The correction is simple: We're already reading video metadata,
including the timestamp of the first frame, so we just have to apply
a correction during video processing to undo the frame timestamp
offsets in the video file.

Improve the interaction between multiuser and cursors

Include missing classes in AIR client

Updates for the 2.1 AIR client

 - drop whiteboard and cursor messages instead of enforcing rights ma…

Minor AIR updates for 2.1 chat

 - hide broadcast layout button for viewers

 - exclude pencil draw update and end status from being dropped by rights management so that pencil lines will smooth out

Prevent duplicate wav files

Fix updating of config.xml

Fix group chat

First pass at chat in the AIR client for 2.1

 - put logos into its own directory

Merge branch 'moderator-message-ui' of https://github.com/riadvice/bigbluebutton into riadvice-moderator-message-ui