When a new block is rejected by the validation pipeline as orphan,
the chain now keeps it in a ring buffer of capped size. Anytime
a new block is accepted, all orphans in the ring buffer are
retried. This is helpful to handle all the cases where we receive
blocks out of order for networking/timing reasons.
* Adding cuckoo-miner into grin as a proper dependency now
* Defaulting to using cuckoo-miner
* Updates to tests to use cuckoo_miner by default, (using cuckoo16)
Introduce a new Chain struct that maintains the current head,
acts as facade to the store and the block processing pipeline
and handles all appropriate locking.
All higher level components, like the overall server, REST APIs
and miner have been update to only depend on Chain. Cleaned up
some duplication and tests now that there's a single entry point
to all blockchain operations.
