[Done for V0.36] ACTION_OBJECT_CONVERT actions

[Sophia]

This action would work similar to the other OBJECT_ actions, affecting all objects of a specific type, only, this one would be aimed at items, as opposed to static dungeon objects.

When one of these actions was executed, all objects matching the specified type would convert in the appropriate way.

Some possibilities:
- Bombs with remote detonators
- Spells that appear to teleport stuff around

[George Gilbert]

Done for V0.36

(actually, I've added an ACTION_SWAP_ALL which will swap object types for any object in the dungeon which is a bit more general than forcing a convert).

[Sophia]

The name might cause some confusion given that it used to do something else, but otherwise, that is even better!