Some fixes for 5.2

[initsu]

• VoD trap tile path logic no longer accepts "NONE" terrain as walkable paths, as it can be filled by anything by GrowTerrain
• Fix RoomPool error if it tried to sample item rooms from empty weights (could happen with smaller room pools and duplication protection)
• Fix Helmethead's vanilla HP bar. Sometimes Helmethead's HP bar would start at half (if swapped to the East I think)
• Vanilla-Weighted palace style removed from GP options as it doesn't do much differently from Random Walk for GP.
• Added more aggressive caching for the web app. This is GitHub specific. It's a workaround for the app potentially being cached for only 10 minutes if another CDN node served the next page load.