Fixes#1082:
This commit allows recovery of a wallet from a seedphrase
with a new endpoint wallet/recover. 4 parameters are passed in,
the same three as for wallet/create but also a bip39 seedphrase
as the fourth argument.
This commit also adds a rescanblockchain RPC call and status:
This adds a new endpoint /rescanblockchain which is (Core) wallet specific
(due to underlying JM architecture). This action is spawned in a thread,
since the bitcoind RPC call is blocking and can take a very long time.
To monitor the status of the rescan, an extra field `rescanning` is
added to the /session endpoint.
Also adds test of rpc wallet recovery
Adam Gibson
7f4eaa9846