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.
Rather than the main package being responsible for opening the address
and transaction managers, the namespaces of these components are
passed as parameters to the wallet.Open function.
Additionally, the address manager Options struct has been split into
two: ScryptOptions which holds the scrypt parameters needed during
passphrase key derivation, and OpenCallbacks which is only passed to
the Open function to allow the caller to provide additional details
during upgrades.
These changes are being done in preparation for a notification server
in the wallet package, with callbacks passed to the Open and Create
functions in waddrmgr and wtxmgr. Before this could happen, the
wallet package had to be responsible for actually opening the managers
from their namespaces.
StartWithdrawal now persists the WithdrawalStatus before returning, and also
returns a previously saved one in subsequent calls with the same parameters.
