Added ability to choose which output to use

[ErikReider]

Supersedes: #64

Fixes: #62

• [x] Choose monitor as config option
• [x] Notification window logic
• [x] Control center logic
• [ ] Test if disconnecting monitor breaks this
• [ ] Update man page
• [x] Open on focused monitor if the chosen display isn't found

[ErikReider]

Need to investigate segfault. Steps to reproduce:

1. Set output to second monitor
2. open CC
3. disable/unplug output
4. CC + blankwindows should disappear (should do this????)
5. Toggle CC (need to also try opening and closing instead of toggling)

[ErikReider]

Will try to squeeze this in after the GTK4 port if it's stable enough

[nebunebu]

Was there progress made on this?