Investigate re-enabling a tweak if it doesn't fix the framerate

[gkjohnson]

Right now the tweaks are organized in a way that allows them to be enabled and disabled in a linear fashion but it's possible that tweaking something won't actually help the framerate at all. The effect is left running at a lowered quality, though. It would be nice if an effect could be re-enabled if it appears to have little-to-no measurable effect on the framerate.