v2 of channel establishment, in the accpeter case, now sends 2 messages
to our peer after saving the information to disk (our commitment
signatures and our funding transaction signatures)
v2 channel open uses a different method to derive the channel_id, so now
we save it to the database so that we dont have to remember how to
derive it for each.
includes a migration for existing channels
This means some files get renamed, and I took the opportunity to clarify
our naming (the *d* is important!)
1. channeld/channel_wire.csv -> channeld/channeld_wire.csv
2. channeld/gen_channel_wire.h -> channeld/channeld_wiregen.h
3. enum channel_wire_type -> enum channeld_wire
4. WIRE_CHANNEL_FUNDING_DEPTH -> WIRE_CHANNELD_FUNDING_DEPTH.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
