Get rid of the 'movement_idx', since we replay events now.
Since we're removing a field from the 'coin_movement' event emission, we
bump the version type.
Changelog-Updated: `coin_movements` events have been revamped and are now on version 2.
Adds a new plugin notification for getting information about coin
movements. Also includes two 'helper' notification methods that can be
called from within lightningd. Separated from the 'common' set because
the lightningd struct is required to finalize the blockheight etc
Changelog-Added: Plugins: new notification type 'coin_movement'