Add custom FPS option

[CornerPin]

Replaces Limit30FPS, Limit60FPS, Limit120FPS, and Limit144FPS FPS modes with LimitCustom and adds a new option which allows players to set a custom FPS cap between 10 and 1000 FPS. The option is disabled if the FPS limit is set to anything other than LimitCustom.

Resolves #993, resolves #1254, supersedes #1255.