Change Background Dim in the editor to a slider or add a 100% option

[MattRBX]

Having background dim at all is really nice, but I want to completely dim the background just like most do during gameplay.

[peppy]

This implies that you're choosing a beatmap background that you wouldn't be happy to play with? The idea of not allowing 100% dim is that, as the mapper, you are aware of what you are exposing players to when they play the beatmap with default settings.