Test pattern playback event.
Add functionality for finding a song of a pattern instance.
Extend playback position validity checking to support pattern playback.
Implement pattern playback mode.
Add pattern playback button icon.
Add pattern playback button icon to the list of valid icon names.
Add pattern playback support to the controller.
Add pattern playback support to the UI model.
Add pattern playback button to the view.
Prevent jumping to a new pattern instance in pattern playback mode.
Test playback of a zero-length pattern.
Play zero-length pattern only once in pattern playback mode.
Fix jumps breaking pattern playback state.
Merge pull request #267 from kagu/pattern_playback

Pattern playback