[New Feature] Quickly delete multiple/all styles

[Kennnnnnji]

• Browser: Chrome
• Operating System: x
• Stylus Version: 1.5.11
• Screenshot: x

When one has 50+ or even 100+ styles installed, it's really hard to delete them one by one.

[siffegh]

Yes please :-) Related: #533.

[narcolepticinsomniac]

@Mottie had bulk actions working decently in #636 at one point, IIRC.

It sat for too long though, and the last rebase has as many bugs as features AFAICT.

[tophf]

Duplicate of #533.