Fix updating progressColor
Configurable progress bar colors and thresholds
Fix shift-clicking creating zero-sized piles

The count would decrease, but if zero the item wasn't deleted, causing
new items to stack with this "phantom" item and take its tags. Annoying
problem with mutability, making me reconsider immutability.. https://github.com/deathcap/itempile/issues
Render zero-count piles

Normally should not exist, but sometimes do for merging purposes.
Render these instead of hiding them to help diagnose issues whenever
they crop up. Related https://github.com/deathcap/itempile/issues/1