Support .WAV file markers in the VSE and Dopesheet

This can be used to let's say, time your lipsync based on a longer audiofile and directly cut it to that point with no issue when doing character animation. It's also just nice metadata to support in general.

Usecase example:

being able to use those markers with the pose library to put a quick mockup of a film for a sweatbox.

Another usecase:

Being able to spend less time on finding where your sounds are supposed to sync based on pre-given information.