Experimental: begin work on platform bridging

Essentially just abstraction of the EchoPet API for independence from
the Bukkit API – possibly for allowing expansion to other server
platforms (Sponge, Glowstone, etc.)
Reduce navigation speed
Add and remove pet ID appropriately
Improve handling of certain commands
Begin drafting a bridging system (mostly for entities)
Merge branch 'bridge' into 3.x