Implement bumping engine in ChannelMonitor::block_connected

Add RBF-bumping of justice txn, given they are only signed by us we
can RBF at wish.

Aggregation of bump-candidates and more aggresive bumping heuristics
are left open

Fix tests broken by introduction of more txn broadcast.
Some tests may have a relaxed check (claim_htlc_ouputs_single_tx)
as broadcast bumped txn are now interwining in previous broadcast ones
and breaking simple expectations

Use bumping engine to rebuild claiming transaction in case of partial-
claim of its outpoints set.

Author: Antoine Riard