Expose channel payment was received on in events

[TheBlueMatt]

And while we're at it expose current confirmation count in ChannelDetails

[TheBlueMatt]

Tagged 113 as its a user request

[tnull]

Can pick this up as a follow up to #1790, since it should probably use user_channel_id?

[TheBlueMatt]

Yea, makes sense. I'd think we should do both channel_id and user_channel_id.