Add channelId to websocket event

[t-bast]

Thanks to recent changes, the channelId is available in ChannelStateChanged.
We now propagate this information to websocket channel events.

[codecov-io]

Codecov Report

Merging #1605 (be4e485) into master (54b589c) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1605      +/-   ##
==========================================
- Coverage   87.33%   87.32%   -0.01%     
==========================================
  Files         146      146              
  Lines       11058    11058              
  Branches      471      471              
==========================================
- Hits         9657     9656       -1     
- Misses       1401     1402       +1     

Impacted Files	Coverage Δ
...cinq/eclair/blockchain/bitcoind/zmq/ZMQActor.scala	90.00% <0.00%> (-5.00%)	⬇️
...q/eclair/blockchain/electrum/ElectrumWatcher.scala	76.98% <0.00%> (-0.80%)	⬇️
...nq/eclair/blockchain/electrum/ElectrumWallet.scala	80.25% <0.00%> (-0.26%)	⬇️
...c/main/scala/fr/acinq/eclair/channel/Channel.scala	86.06% <0.00%> (+0.08%)	⬆️
...cala/fr/acinq/eclair/payment/relay/NodeRelay.scala	95.27% <0.00%> (+1.57%)	⬆️