Forge Permissions API

A simple permissions api which allows mods to check for permissions and
permission providers to hook in and provide their results.

To check a permission, a mod simply calls
```
result=ForgeEventFactory.checkPermission(player, "some.permission");
```
If result is not DENY, the permission was granted.
The permission sytax should be similar to the one bukkit is using.

Permission providers can hook to the ```MinecraftForge.PERMISSIONS_BUS``` event bus and modify the result accordingly. 

Additionally, there is a LocatablePermissionEvent class for area-based permissions.