Fix audio height in 100% mode

This changes the way the audio player works in the 100% width mode.
Since audio elements don't actually have a height, the controls are
the only height to the audio element. This makes it so the audio
player will still be the height of the controls if the progress is
set to autosize.
Merge pull request #667 from dougwilson/fix/audio-auto-width

Fix audio height in 100% mode