Clipboard support

[l4l]

It might be handy to support clipboard.

• Copy, as far as I know, won't work, because no other wayland client can get a buffer after exit. And since yofi is displayed as overlay no other window (except locking screen maybe) can get it. Therefore I don't feel like it make much sense to implement it.
• Paste should work fine.

[WhyNotHugo]

Copy would make sense if someone were using a clipboard manager.

However, there’s no functional clipboard manager out there, so that’s not really relevant yet.

[l4l]

Yeah, that's right, thanks for noticing. It seems there's one: https://github.com/yory8/clipman