Improve click detectors

Introduce "gadgets" as a structural function, for items that can be used
when held and when not held. Click detectors are such an item. Make
click detectors correctly attach and use up batteries when used.

src/Dodge/Creature/Impulse/UseItem.hs

@@ -32,6 +32,10 @@ useRootItem crid w = (worldEventFlags . at InventoryChange ?~ ()) . fromMaybe w
             return $
                 heldEffect (bimap _iatType fst3 itmtree) cr w
                     & pointerToItem itm . itUse . heldHammer .~ HammerDown
+        GadgetPlatformSF ->
+            return $
+                heldEffect (bimap _iatType fst3 itmtree) cr w
+                    & pointerToItem itm . itUse . heldHammer .~ HammerDown
         EquipmentPlatformSF -> do
             guard (_crHammerPosition cr == HammerUp)
             invid <- itm ^? itLocation . ilInvID