Add notes field on detailed channels tab

[Bitcoinite]

We already have the possibility to add notes on the /opens tab. It would be great to also add notes for every channel on the detailed channels tab.

Especially for larger nodes, this would help a lot with monitoring channels over time.
This could also be enhanced by adding labels (sink/source/router) to the channels, maybe as boxes we can check.
This information could then be used for AF, AP and maybe more advanced AR in the future.