hard update 17 changes

[zack-bitcoin]

what functionality changed

After this update it will be possible to publish multiple channel offers from the same account, and it is possible for multiple of them to be accepted.
Currently if one is accepted, all the others become invalid.

channel close requests had the same problem, it is also fixed.

what code changed

1. a new transaction type channel_team_close_tx2.
   It has a few changes from channel_team_close_tx.

• Now the tx says how much money is going from the channel to each account, which makes it easier to do block explorers.
• this tx does not update any nonces.
• the tx has lower and upper block height bounds, it is only valid if it is published between the bounds.

2. we don't delete channels any more. now instead we flip the bit to say that this channel is inactive.

3. we updated all the channel tx types so they check that a channel is open before operating on the channel.

4. new_channel_tx2 no longer updates the nonce of the account that created the tx. This way you can make multiple channel offers at the same time, and more than one can get accepted.

[zack-bitcoin]

b992b95
hard update 17 is going to be activated around May 23 at block 66775