moveing auto generated protobuf glue into meshtastic.protobuf.

[geeksville]

Related to #579. What about moving the generated protobuf glue out of the root of the meshtastic project. Instead have it in meshtastic.protobuf. Do ya'll (in particular @ianmcorvidae) think that's a good idea?

If so, I can send in a PR soonish.

It will be a breaking change if there are any external users of our API that have reached in and touched those classes (though I didn't find any in my googling).

(Also I'm sorry I didn't do this originally before there was so many great folks using/improving this - it would have been less painful if they were in the right place all along)

[ianmcorvidae]

I think this is a good idea.

I do know there's some folks who are importing the _pb2 modules directly in order to use them (particularly folks who are pulling stuff straight off MQTT). I think we can just be sure to mark it clearly in the release notes when we do it. It's not a huge change to stick in the extra folder in imports, so it shouldn't be a painful migration for anyone I don't think.

[geeksville]

done!