This commit saves the RPC request used to construct the `Parameters` on
disk. Since it's a proto message, an easy way to read/write it is to
rely on the proto marshal/unmarshal methods. A side effect is that
migration also becomes easy as proto message have its own internal
mechanism to keep track of the compatibility.
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.
This allows Loop users to further improve their privacy by not revealing
their source IP address. Note that the identity of the lnd node behind
Loop can still be revealed when performing a Loop In due to the swap
server extending an off-chain HTLC to the user.
Onion addresses don't yet exist for the swap servers, but they will be
added at a later time.
