Issue and Steps to Reproduce

@cdecker sorry for the long list, the following methods could really help me out.

Please add/build out new gRPC methods:

• ListClosedChannels
• openChannelAbort
• fundChannelCancel
• multiFundChannel
• broadcastChainTransaction

Subscriptions:

• staticBackups
• forwards
• channel events (opens/closes)
• payments (send/receive)
• chain transactions
• Subscribe to probes