To decide whether we event want to attempt a swap, we add a fee limit
that we check against our estimate for the current number of
confirmations we want our sweep to confirm in. If fees are higher than
this limit, we do not suggest swaps.
This commit updates swap suggestions to return loop out requests with
sufficient fields populated so that a loop out can directly be
dispatched from a suggestion. This requires setting of fees an min
sweep conf targets (our htlc conf target and addresss will be set by
the daemon's client rpc server if we do not provide them). We also do
some test refactoring so that we can more easily test the suggest swaps
endpoint.
