Various ItemMeta fixes.

Fixes BUKKIT-3408, BUKKIT-3190, BUKKIT-3191, BUKKIT-3407

These changes relate mostly to semantical changes for serialization
contract, exception of changing the map scaling value from byte to boolean,
what it should have been in the first place. Appropriate unit tests were
added for CraftMapMeta, as they were missing.
Spawn monsters without prematurely exiting. Fixes BUKKIT-3425

By using return 0, we exit the loop prematurely preventing other
creature types from being spawned if one type is set to 0. By using
continue we move on to the other types and allow them to spawn
properly.
Add ItemStackMapTest

This test was missing from c056293b38cb9a1296937d91746b175252be044a
Throw BlockPlaceEvent when placing double slabs. Fixes BUKKIT-2469
Handle beds and doors the same way as other blocks. Fixes BUKKIT-3437
Relates to: BUKKIT-3438
Merge remote-tracking branch 'upstream/master'