Improve PermFactory inheritance.#20

I would like to see a simplified version of PermFactory, maybe even as an extended class. At the moment, if I am to create a permission 'prefix.cmd.parent'. I'd type the following: ``` java PermFactory.newPerm(clazz, "cmd.parent").commandPermission().usePluginName().build(); ``` That doesn't look too messy... but now, I want to make a child permission to the 'prefix.cmd.parent' permission node called 'prefix.cmd.parent.child'. ``` java Perm parent = PermFactory.newPerm(clazz, "cmd.parent").commandPermission().usePluginName().build(); Perm child = PermFactory.newPerm(clazz, "cmd.parent.child").commandPermission().parent(parent).usePluginName().build(); ``` What I hope to implement is something like: ``` java Perm parent = PermFactory.newPerm(clazz, "cmd.parent").commandPermission().usePluginName().build(); Perm child = SimplePermFactory.newPerm(clazz, "child").parent(parent).build(); Perm childBaby = SimplePermFactory.newPerm(clazz, "baby").parent(child).build(); // Yields prefix.cmd.parent.child.baby ```