Simulate position with coordinator

[holzeis]

The maker does not actually setup a dlc with the coordinator as it is a trusted setup. Accordingly the maker will simply create a simulated position in his database once the coordinator setup the dlc with the taker.

This position will always be updated contrary to how the coordinator manages its positions which are always inserted newly on open trade.

Additionally, PnL should be exchanged between the two players regularly, i.e. if the simulated position resulted in a loss for the maker, the maker should pay the coordinator (and vice-versa).

[luckysori]

Additionally, PnL should be exchanged between the two players regularly, i.e. if the simulated position resulted in a loss for the maker, the maker should pay the coordinator (and vice-versa).

I suppose we could leave this out of the scope of this ticket. The maker can keep track of the PNL (and the coordinator too?), but we don't have to apply the changes until we have a channel in place (added with #926).