Allow users to add secondary thresholds to the bar that behave like the Devouring Plague threshold does currently, but are configurable for different values.

Stretch goal: possibly move Devouring Plague to use this system.

With the Options tech added for #87 , this probably wouldn't be difficult to add now.

Simple case:

• Set threshold to a specified resource amount.
• If the resource is at or over the specified amount, turn it green. Otherwise, white. (default colors)

Intermediate case:

• Set threshold to a specified resource amount.
• If the logic check for activation (using the same piping as bar text) passes, turn it the specified color. Otherwise, white (default colors)

Advanced case:

• Set threshold to a specified resource amount based on logic checks.
• Multiple logic checks for activation (using the same piping as bar text) passes, turn it the specified color. Rank these in order of precedence. If none pass, white (default colors)

Marksmanship Hunter implementation moves towards this by shifting from individual properties for thresholds to an array and does dynamic loading based on cooldown/talent/resource level.