Name the tilesets and give them constants.

Also clean up the tileset macro and remove placeholders/redundant files.

constants/tilesets.asm

@@ -0,0 +1,25 @@
+OVERWORLD    EQU 0
+REDS_HOUSE_1 EQU 1
+MART         EQU 2
+FOREST       EQU 3
+REDS_HOUSE_2 EQU 4
+DOJO         EQU 5
+POKECENTER   EQU 6
+GYM          EQU 7
+HOUSE        EQU 8
+FOREST_GATE  EQU 9
+MUSEUM       EQU 10
+UNDERGROUND  EQU 11
+GATE         EQU 12
+SHIP         EQU 13
+SHIP_PORT    EQU 14
+CEMETERY     EQU 15
+INTERIOR     EQU 16
+CAVERN       EQU 17
+LOBBY        EQU 18
+MANSION      EQU 19
+LAB          EQU 20
+CLUB         EQU 21
+FACILITY     EQU 22
+PLATEAU      EQU 23
+