[Feature Request] Add an option to set a custom resolution for UltraCam

[Yr1t]

So pretty much, I'm asking for a toggle so I can set my own resolution in the UltraCam configuration section. I use a 21:9 monitor, and it gets annoying having to edit the .ini file every time I re-merge because the presets assume you have a 16:9 monitor.

Here's a little crappy mockup I made in the screenshot editor to show what I was thinking it could look like: