Merge pull request #838 from TheBlueMatt/2021-03-skip-blocks

Make `Channel`'s block connection API more electrum-friendly

diff --cc fuzz/src/chanmon_consistency.rs
Simple merge

diff --cc lightning-persister/src/lib.rs
Simple merge

diff --cc lightning/src/ln/channelmanager.rs
Simple merge

diff --cc lightning/src/ln/functional_test_utils.rs
Simple merge