organise bzz code into subdirectories

• api, storage, network and services contain go subpackages
• split off netStore into chunk store logic in storage subpackage, protocol handler logic and cloudstore backend in network.
• NetStore now lean, only shared cloud access logic implementing ChunkStore Interface. Dispatches to a CloudStore implementation
• DpaChunkStore local access logic to swarm implementing ChunkStore Interface
• network.forwarder implements bzz cloud backend logic (forwarding, propagation, delivery), uses the peers syncer for queueing and Hive for routing/forwarding
• network.Depo implements network.StorageHandler. remote access to swarm. handler for incoming storage/retrieval-related messages e.g. coming from bzz protocol. passed via swarm->protocol->depo depo dispatches to storage.NetStore
• lots of renaming, rename bzz to swarm
• Hive now acts as peers msg handler
• dbAccess now encapsulates dbStore iterator and counter access used by syncer passed via swarm->protocol->syncer
• unsyncedKeys and delivery request handling now out of syncer in depo
• cmd directory now contains bzzhash and bzzup
• services contains swap accounting, swear (was bzzcontract)
• examples contain album (was demo) and httphandler
• the PR also fixes several sync issues
• uptodate develop