Various field/belt related stuff

- Remove all field booleans except quickfire and belt, which have been moved to cCurTown
- Alter and extend place_spell_pattern, to allow arbitrary damage types and to make it more clear in the code what's happening when it's called
- Delete fields.cpp file; a few things moved to locutils.cpp, but most are now part of cCurTown
- set_terrain function automatically updates belt present boolean if setting to a conveyor.

osx/boe.items.cpp

@@ -13,7 +13,6 @@
 #include "boe.items.h"
 #include "boe.specials.h"
 #include "boe.party.h"
-#include "boe.fields.h"
 #include "boe.locutils.h"
 #include "boe.newgraph.h"
 #include "boe.itemdata.h"