Update hotkey button css to maintain constant button height
Handle player corner case - error if trim buttons were pressed during audio load

The trim buttons are based on the current loaded audio duration to ensure accurate
trimming. If the player was mid-loading, it's duration property is invalid. Pressing
a trim button during this state would cause an invalid time to be registered.

This patch ignores trim button presses unless the audio is loaded with a valid
duration property.
Modified AJAX http requested to gracefully handle non-200-OK response
Support multiple clip deletion
Bugfix - assign_clips - missing argument in javascript attribute assignment
assign_clips : comment out clip row delete link

This has been superceded by row select checkboxes and a 'delete selected'
link, which was requested in user feedback.

This makes it less easy to accidentally delete clips, but adds
an extra mouse click to any deletion. Only commented out to make it easy
to put back in if user opinion changes!
Add recording checkboxes to channel list (not yet operational)