[Bleeding] Handle players disconnecting during respawn. Fixes BUKKIT-4327

Prior to this commit, a player disconnected during a respawn event would
remain in memory. This causes a ghosting issue of players in the slot
count and player list, as well as a reference leak.

This commit avoids re-adding the player to the player list (and world) if
they are disconnected. This ensures that the remainder of the respawn
logic is completed as well as ensuring a duplicate player is not left on
the server.

This commit also saves the player's file at the end of the method if they
have been disconnected to ensure that their next login is accurate to the
respawn event's actions. A player that was revived and disconnected will
reconnect as revived.
Implement SpawnReason.NETHER_PORTAL and DISPENSE_EGG. Fixes BUKKIT-3148

Previously any entities spawned through dispensers (monster eggs) or
by nether portals were given the incorrect SpawnReason of SPAWNER_EGG.
This made it impossible to distinguish what exactly happened in regards
to the creature being spawned.

A method in ItemMonsterEgg has been added to further fine tune reasons
for spawning creatures. This permits the DISPENSE_EGG reason to be used
correctly and accuratly as well as the NETHER_PORTAL reason due to how
BlockPortal spawns the mobs.

The redirected method, a(World, int, double, double, double), is still
called by the ItemMonsterEgg itself and therefore uses the default reason
of SPAWNER_EGG. This does not change previous behaviour.
Update clients when ItemFrame direction is set. Fixes BUKKIT-3371

Hanging entities are placed into the entity tracker and updates are sent
out to clients for the initial placement. Thereafter data watchers are
configured to monitor the item inside the frame. However, if the
direction the ItemFrame facing changes the entity tracker will not send
out updates.

This commit removes and recreates the ItemFrame entity in the same way
that was already done for Painting entities. This causes clients to
be updated appropriately.