Simplify the MCM experience

Instead of presenting all the settings front and centre, make the preset selection screen the primary view, but add an additional one that reflects our current default settings.

Consider renaming presets to Low -> Epic to reflect typical in game performance settings. Consider adding a description field to each config xml to allow updating the descriptions without a new MCM

In the default custom config view, switch most settings to a Low to Ultra slider, with the numbers abstracted away.

Advanced users can edit the xml, or we can add a advanced setting that displays the numbers with no slides for easier entry.