Fix for very unlikely Graveyard problem; Lucky Blocks example config; thunt delete fix

- Fix for graveyard with no named graves in which to bury treasure in (very unlikely but possible)
- Add sample config that adds "lucky block" objects in loot, with example of generic and custom versions.  This needs to be tested.
- 'entrance' null data member added to treasure_hunt object to ensure compatibility with dungeon utility functions
- in mcdungeon delete reload cache if no dungeons *and* no thunts to deal with situation where you have existing treasure hunts but no dungeons, else you cannot delete treasure hunts