Add organization to PermissionManagerGUI

[squareblob]

Permissions should be sorted by plugin. There should be dividers for readability. Current behavior requires a lot of needless hovering over items:

[Maxopoly]

As part of this I think it'd also be good to use an item to visualize each option and enchant the item if that group has that permission. Don't put too much effort into the GUI of this branch though, as all of that is getting rewritten anyway.