Separate cutting from deleting

This is similar to https://feedback.getrecut.com/feature-requests/p/keep-silent-segments-in-xml-exports but with the goal of having 3 states that a segment could be in:
- Audible: It gets left in, has cuts around it
- Silent + Kept: Gets left in, has cuts around it (treated as audible)
- Deleted: Gets completely removed during export
Right now there are only 2 modes, either audible or silent, and when you "restore" a silent section by hitting Backspace, it gets merged in with the audible sections on either side of it. It'd be nice for some use cases to be able to leave those cut points intact. (e.g. for being able to speed up silent sections of typing in a screencast).