This updates all code to make use of the new chainhash package since the
old wire.ShaHash type and related functions have been removed in favor
of the abstracted package.
Also, while here, rename all variables that included sha in their name
to include hash instead.
Finally, update glide.lock to use the required version of btcd, btcutil,
and btcrpcclient.
Doing that may cause erratic test failures when we run them in parallel, so
move the functions the tests need to mock as struct fields that are not
shared across tests.
StartWithdrawal now persists the WithdrawalStatus before returning, and also
returns a previously saved one in subsequent calls with the same parameters.
