Review Lightning architecture & API

[carmocca]

 Document: https://docs.google.com/document/d/1xHU7-iQSpp9KJTjI3As2EM0mfNHHr37WZYpDpwLkivA/edit#

[edenlightning]

@carmocca what is TODO?

[carmocca]

Plan was to write a document with all these things, but many have been covered by @ananthsub 's API review.

Have been using this issue to link all the PR's I've opened testing the hook consistency