parser: IMG4 superblock support

[m1stadev]

Adding in support for IMG4 superblocks (e.g. dumped off disk1 on an *OS device) can serve as an easy method for firmware/IM4M extraction.

Most likely could be done via a Superblock class, that just runs IMG4 on the data internally over & over until it runs out, then just store them all as a tuple under Superblock.img4s

Also should add support for interacting with them in CLI (pyimg4 superblock?)