add /skin skull command

[xknat]

pr continuing where #995 left off

This pr add's the following:
commands:

command	Perms	info
/skull (skinsrestorer:skull)	skinsrestorer.skull	gives your own skull
‎‎/skull get [source info]	skinsrestorer.skull.get skinsrestorer.skull.get.other skinsrestorer.skull.get.url	get yourself a skull
‎‎ /skull give target source info	skinsrestorer.skull.give	give a skull to player
/skull update	skinsrestorer.skull.update	update a handholding skull
‎‎ /skull lock (true/false)	skinsrestorer.skull.lock	lock a skull to prevent auto updating
‎‎ /skull props	skinsrestorer.skull.props	get the properties of a skull

Config:

• Ability to let SkinsRestorer auto update skulls around the world

Locale:
TBD

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todo:
Main

• add more commands (get, give & update)
• add messages to locale
• error handeling
• return feedback if inventory was full to bungee

additional:

• use PersistentDataContainer [video tutorial]