Separated addon.strip.sounds callables

This now distinguishes between an "AwesomeTTS technique" and a "Anki
technique". The former will be usable by most of our code, and will use
a precompiled re object and eventually have more functionality, whereas
the latter will be used by code that needs to emulate something that
Anki does.
Add stripping support

Implements the accept() method for the Stripper dialog.