Added two sets of commands and permissions.

/loot clear (lootgui.clear) - Allows players to clear their own loot
/loot clear [target] (lootgui.admin.clear) - Allows players to the loot of target players.

New customizable messages are also available in the config related to these commands.

Initially the plugin would update the players loot in the config.yml each time an item is added to or removed from the collect menu. This has been changed to use a HashMap to store the players loot, meaning the plugin only reads from the config when a player joins the server and only writes to it when the player leaves the server.

Due to an oversight on my part, the plugin originally used the players name to store their loot in the configuration file. This has been amended to use their UUID instead,