Add optional voxel-registry support, remove global InventoryWindow_defaultGetTexture

If opts.registry is passed, will call getItemPileTexture, as an alternative to opts.getTexture
Check for missing get texture in constructor
Fix crash shift-clicking empty slots with linked inventories
Start adding progress damage bars. Ref GH-9
Create progress node on-demand since apparently DOM appendChild() doesn't guarantee div.children will be updated by the next statement? odd
Show progress bar from (maxDamage - damage) / maxDamage
Add progress bar colors
Fix updating progress width