switched the word close in the audio and video popups with cancel
when options is clicked focus the user list
added pre and post text to the slide in the Flash client
removed the deskshare region button from the tab order
changed the url in the footer to be an actual link
added content headers to playback.html
added checkbox to conditionally expose chat messages to a screen reader
Merge pull request #216 from SenecaCDOT-BigBlueButton/second-round-accessibility-fixes

Second round accessibility fixes