Specify how an eventId should be calculated

[benthecarman]

An eventId should be a unique identifier between the parties in the DLC. Ideally it should be deterministic and should be reliant on the contract as well, to best accomplish this it would likely need to be a hash of the contract info, oracle info, the timeouts/delays, as well as some public keys from the participating parties whether it be each other's funding keys or maybe a lightning public key.

[Tibo-lg]

Ah sorry just opened #32 without noticing this one.

[nkohen]

After further thinking, I ended up proposing in #59 that this should be done the way it is done in lightning (by using the funding output with a temporary id, which I computed as the hash of the offer)