Add standard interfaces for media and iota storage/transfer

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From @kineticneticat:

would it make sense to add an interface to hex thats completely generic and has methods to standardise interacting with media containers? I was messing around with moving media between items, blocks, & entities and theyre all completely different, items have the ADMediaHolder, blocks dont really have anything other than what AbstractImpetus does, and entities like wisps (irrelevant to base hex, but still nice) are also completely different too
a standard interface with methods to get the current media, media cap, remaining media, etc would be nice