Use full file paths for cutscenes, quests, and tilesets

Closes #115
Merge pull request #1067 from dorkster/full_paths

Use full file paths for cutscenes, quests, and tilesets
Allow sloppy dropping of items on to Inventory/Stash/Vendor

Fixes #1060

Other fixes:
- Cached drag icons now have abbreviated quantities like slots do
- Equipment slots are now highlighted regardless of drag source