Sync position with dlc channel state

[holzeis]

Due to an error I am having an open position but a closed dlc. It would be great if the app would be smart enough to sync these states, while the DLC is the source of truth.

if DLC is in SubChannelState::Signed: Create position (take data from order) if not existing
if DLC is in SubChannelState::OffChainClosed: Delete position if still existing

would have been useful for #1257

[holzeis]

Note this will also help if the channel got force closed.

[bonomat]

Please add a MASSIVE TODO that this is not the right way to do it.