Added More Detailed Permissions to Spawner Signs

This PR adds some more detailed permissions for Server Admins to use with Spawner functionality. They are set by default to "True", so, if I am not mistaken, those desiring to not bother with these additions should not have to.

I have tested a compiled jar of it on Bukkit 1.7.2 R0.3 and it works as intended.
Here are the new permissions:
train.spawner.automatic - Enables automatic timed cart creation (e.g. New cart every 5 seconds)
train.spawner.regular - Enables users to create regular minecarts
train.spawner.powered - Enables users to create powered minecarts
train.spawner.storage - Enables users to create minecarts with chests
train.spawner.tnt - Enables users to create minecarts with TNT
train.spawner.hopper - Enables users to create minecarts with hoppers
train.spawner.spawner - Enables users to create minecarts with spawners

Please review this PR and merge as you see fit.