Configurable routing fee limit

[kilrau]

When executing a swap we want the user to be able to configure the currently 3% hardcoded routing fee cap. Currently only applicaple for lightning, we should wait with implementation until https://github.com/connext/vector supports routing fees too.

[kilrau]

The approach we discussed today:

• limit total routing fees to e.g. 0.5% of total trade amount via lnd's sendpayment call
• show routing fees in tradinghistory

wdyt? @sangaman

[raladev]

Can we add sort of option for user to regulate that? @kilrau @sangaman

For me 0.5 is to much if I use small margin option for arby.

So, it would be better to have the RouteFee option which i can set:

1. Dont want to pay RouteFee (0%)
2. Another value (0.5%) - All swaps with fee more then 0,5 of total trade amount should be dropped with RoutingFee error.

But it will work only if we can calculate RoutingFee before swap performing.

[kilrau]

1. this will fail 100%, nobody routes for free
2. 0.5% is just this is just the max cap, in practice your lnd will mostly choose the cheapest option for you automatically. Also, in practice total routing fees are that small that they don't matter so I wouldn't want to make this issue more complicated than it is.