make SpeedModType variable names more descriptive
overhaul custom TimingWindow system

The old system was misleading: a user could change his/her ThemePref value and the TimingWindow OptionRow would no longer accurately reflect the current state of Preferences.ini's timing window values.

This new system compares current Preferences.ini values against static values every time, and determines which (SM5, ITG, Pump Pro, or Custom) timing window set is actually in use.