Clean up unused includes
Use unique_ptr for AudioWaveformRenderer's decode buffer
Don't compile the FFT code if FFTW is enabled
Make video providers report whether their file has audio tracks

Fixes errors when trying to automatically open audio from dummy video
and improves UX a little by disabling the Open Audio From Video menu
item when there are no audio tracks.
Fix crash when opening video

If video was previously open and the user chooses to resample the script
for the new video, VideoController would try to update the subs for the
now-deleted old provider.
Don't clear project properties on undo/redo
Use more plural forms for translatable strings
Return absolute paths for files in project_properties()