Prerequisite changes

• Refactor thresholds setting to put generic properties (e.g. width) into their own sub-table
• Refactor colors.threshold colors into the new color tables
• Standardize the colors in colors.threshold
  • Change mindbender for healers to be something else (shared)

Options UI

• Add a new "Thresholds" tab for all specs (and Global Settings) and move existing thresholds options there
• Make a new function that allows for consistent creation of colors+options. Maybe add a way to pass in custom values (looking at you Shadow Priests and Rogues)?
• Change order of thresholds to be, in order top to bottom:
  1. Ability threshold toggles
  2. Colors
  3. Size/positioning
• Adjust layout of each spec's threshold lines to use both columns
• Add global enable disable to colors and size/positioning