Adds an option to set the video bitrate. Patches provided by Benoît Laniel on the dev@ mailing list (under the subject of '[PATCH] Set default max video bandwidth to 128')

git-svn-id: https://svn.java.net/svn/jitsi~svn/libjitsi@10665 198c5059-ef06-4ec0-9a75-fdd6b0ef00a6