Track ChannelTransactionParameters in ChannelMonitor FundingScope

The `ChannelTransactionParameters` will change across `FundingScope`s,
so we make sure to track it to ensure it is updated accordingly when a
new `FundingScope` is applied/considered.

Along the way, we also clean up some unnecessary function arguments to
`ChannelMonitor::new` that we can just obtain from the
`ChannelTransactionParameters` already provided.

Author: wpaulino