[x] simplify the CIDv0 storage for IPFS metadata to a cleaner storage of sha256 digest of metadata; leaving the IPFS hosting to architecture layer
[x] basic coverage of unit tests of implemented base58 encoding (used for short and long names in NameRegistry)
[x] always have short names be padded to 12 characters (it is unlikely an address would result in a shorter short name), so that there is no visual confusion about length of short names
fixes #143