Fix Monster Spawners

[95CivicSi]

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Pull Request description

This will fix several existing bugs with Monser Spawners where the mob being spawned doesn't show up inside the Monster Spawner and server restarts can cause the Spawner to stop working.

Changed Branch

Master

Optional information

Details of what was changed are included in each commit message. Most notable are:

• Addition of a new block class: MonsterSpawnerPEX
• Refactor of Spawner to MobSpawner
• Update MobSpawner::setSpawnEntityType

The biggest complication here was that the game client displays the mob inside the Monster Spawner based on the NBT of the MobSpawner tile. Because the MobSpawner class was previously called Spawner, game clients didn't recognize the NBT Tag id as a spawner.

[samuelctn]

gj