refactor(blockstore) mv under blocks/

@jbenet @whyrusleeping

the pyramids were built one brick at a time

addresses: https://github.com/jbenet/go-ipfs/issues/370

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>
rename

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>
rename exchange

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>
refactor(blockstore, blockservice) use Blockstore and offline.Exchange

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>