Closes#274. Utxos are disabled if they are sent
to a reused address, and are below a threshold
set by the value `max_sats_freeze_reuse` in the
`POLICY` section of the config file. If the value
is -1, such utxos are always frozen irrespective of
the value.
Users are prompted with a warning level logging message
on CLI and a popup on Joinmarket-Qt. Such disabled utxos
can of course be re-enabled by the existing methods.
Also adds test case for address reuse freezing function.
Adam Gibson