This addresses a user-reported issue where Low Threshold was not usable with Color By Health/Mana % disabled, due to some internal technical reasons. This was exacerbated by the recent fix that allowed Low Threshold and Color By Health % to work together.
This also fixes the low threshold flash to apply immediately when changing the option, and fixes the Low Threshold % slider to be usable without the Low Flash option set.
Finally, it hides the Low Flash option for bars that don't support it (right now that's just PlayerMana, I think because it only sets the low threshold to the Min Mana Color even if the class uses a different power type...something for future me...).
Fixes wowace ticket #334
c5c44edf64
