ChainInterface is easy to misuse

[TheBlueMatt]

In writing https://github.com/TheBlueMatt/rust-lightning-bitcoinrpc I almost misused ChainWatchInterface, almost calling ChannelManager::block_connected and PeerHandler::block_connected instead of only calling ChainWatchInterfaceUtil::block_connected (which will call the others for you).

I'm not actually sure what a better interface looks like. I played around a bit with making some things pub(crate) in chaininterface but couldn't come up with anything I actually liked, sadly.

[dongcarl]

I played around a bit with making some things pub(crate) in chaininterface but couldn't come up with anything I actually liked, sadly.

What was insufficient with pub(crate)?

[TheBlueMatt]

We don't have a ChainWatchInterfaceUtil anymore, and this interface is much much harder to mis-use now.