This commit adds a reset() closure to the kvdb.View function which will
be called before each retry (including the first) of the view
transaction. The reset() closure can be used to reset external state
(eg slices or maps) where the view closure puts intermediate results.
When a remote peer claims one of our outgoing htlcs on chain, we do
not care whether they claimed with multiple stages. We simply store
the claim outgome then forget the resolver.
Incoming htlcs that are timed out or failed (invalid htlc or invoice
condition not met), save a single on chain resolution because we don't
need to take any actions on them ourselves (we don't need to worry
about 2 stage claims since this is the success path for our peer).
Add a new top level bucket which holds closed channels nested by chain
hash which contains additional information about channel closes. We add
resolver resolutions under their own key so that we can extend the
bucket with additional information if required.
