Add 'Well' landmark, fix 'Cottage' landmark and 'FlowerGarden' landmark

Add new THunt landmark -- 'Well' with hidden underground treasure room.
Fix render bug in Cottage that kept removing the floor.
Fixed problem with double-height flowers in FlowerGarden
Correct typo in paintings/Chess_Kight.txt (it's 'knight', not 'kight') used by Memorial landmark
Maybe fixed landmark clearing tree-deletion code?  Hard to test :(