Pass around newly created AudioTimingControllers in a unique_ptr
Use more make_unique
Trigger the audio selection change logic when switching timing controllers

Results in the display seeking to the active line when audio is opened
(if seeking to active line is enabled), and initializes the scrollbar
properly.

Updates #1732.
Make double-click in the edit box smarter

Use the syntax highlighting's word splitting to decide what to select so
that double-clicking on \Nword only selects 'word'.