Code Cleaning

1. Cleaned up some spacing and unused imports in EventHookContainer.
Also changed an indirect reference to BaseItemDoor.trytoPlaceDoor() to a
direct reference seeing as the function is static and should be accessed
that way.
2. Renamed getDoortoItemMapping() to getDoorBlock(). The original named
had a minor capitalization mistake and implied that it would return a
mapping table or would associate doors to items. The function actually
associates items to door blocks.
Changed Door Item Mapping Code

1. Changed EventHookContainer to remove a check against
BaseItemDoor.getDoorToPlace().  The checks performed there can be done
in BaseItemDoor.tryToPlaceDoor(), which removes the need for callers to
know more internal details about how doors are handled. I moved the
checks inside.
2. Renamed vanillaDoorMapping to doorItemMapping. It now maps dim door
items to themselves to remove the need for various checks we were
performing. Updated BaseItemDoor's constructor to reflect this change.
3. Removed BaseItemDoor.getDoorToPlace() and integrated its
functionality into BaseItemDoor.tryToPlaceDoor().
4. Changed BaseItemDoor.tryToPlaceDoor() so that it simply returns false
if a given item stack cannot be used to place any doors. We don't need
to check if the item is an ItemDoor or anything like that now.