Remove shell scrollbars and improved mdiCanvas height binding

MainApplicationShell mdiCanvas height binded to the application height instead of its parent heignt.

Changes to the LTI componet

Changes to the LTI componet

MainCanvas height binded to its parent to avoid using percentHeight.

identify if user is on mac and chrome and show the warning during deskto...

properly resized presentation file list, centered file format hint text ...

 - don't send a StopEchoTest ocmmand and HasAudio event when the user clicks "Yes" on the echo test step. This causes a race condition
   as the StopEchoTest handler just hangsup the call white the HasAudio event, hangs up then calls into the conference.

 - fix issue where a user is duplicated when calling in because the 3rd-party app passed an external userid