witnesses, registering witness url.
Derive memo, witness, etc. keys from the active key.
Make witness_create_operation accept relative key identifiers.
Prevent wif_to_key from throwing on invalid base58 input.
Make witness_node accept witness keys in WIF format.
This reverts commit 8db1b930f3.
Since cli_wallet itself makes no effort to be stateless, we
can simply unlock in a separate call. Removing the ability
to use the header to unlock reduces the potential for user
confusion about whether the HTTP API provides security
(it does not).
