Make use of `syncObjectives`

[andrewgordstewart]

Why: Problem description 😕

Currently, the ChannelManager has no recourse if a message containing an objective gets dropped in transit. This means we can get stuck waiting for another participant to take action on an objective.

What: Describe the solution you'd like ✨

We should make use of the new SyncObjectives method and call it whenever we have an objective that has progressed for some period of time.

[lalexgap]

The solution described can probably be fleshed out more once we start using first-class objectives.