New message type naming and numbering

[fjahr]

Naming and numbering of the new message types are far from final. Happy to receive feedback on the names chosen for our specific messages. Specifically, some sound very similar which might be confusing.

All new message types currently don't have numbers, you will find the placeholder XX instead. The reason is I was unsure if I want to reassign numbers that were given in the original lightning RFCs. I was instead thinking about counting down from the top of the specific number space or opening a completely new number space just for MW specific messages.

[fjahr]

Here is an ordered list of all message types of the original Lightning RFCs: https://gist.github.com/fjahr/479c03e2bdafef984829b5e7b42f6e4d

[fjahr]

And here a list of all message types in Lightning MW: https://gist.github.com/fjahr/67b006100d66577baa0867811f9cc870