Add the ability to hide other ui elements

[ALazyMeme]

In reference to this: https://discord.com/channels/253897423439659008/459650160658481152/874587792930394122

Basically the user has a streaming pc and wishes to show chatterino on screen, but they want to be able to hide everything. Including the titlebar and channel headers while also being able to move and resize the window. Below is the example they cropped:

[Felanbird]

Wouldn't this just be easily handled with ctrl + u and window capture?

[ALazyMeme]

They use a second PC with a capture card, so window capture isn't possible

[pajlada]

This could be solved by running Chatterino on the streaming PC (the PC that OBS runs on) and crop it there with window capture.

[apa420]

Just crop chatterino in OBS?

https://i.nuuls.com/RRKyB.mp4 wow it just works!

[ALazyMeme]

They use a capture card with a second pc, so cropping isn't an option.