Add special nodes that hook into the spell targeting system

- Node to initiate targeting mode and call a special once targets are chosen
- Nodes to place a spell pattern (one for fields and one for booms)

rsrc/strings/specials-opcodes.txt

@@ -197,9 +197,9 @@ set-lighting
 set-attitude
 set-center
 lift-fog
-
-
-
+start-target
+spell-pat-field
+spell-pat-boom