Bring bep protos up to date and refactor a related proto

[imsodin]

I updated the main proto and checked whether the code needs any updates due to that, which doesn't seem to be the case. The repository proto seemed to contain a lot of stuff, that is never used in syncthing-java or syncthing-lite, so I removed it or replaced it with appropriate structures from the bep proto.

It builds, but I didn't build syncthing-lite with it (at least I am not sure whether I did) or test it in any other way. So don't merge unless you actually tested it or just use the parts needed/useful.

[Nutomic]

I'm getting this error when I try to build the Android app:

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:transformResourcesWithMergeJavaResForDebug'.
> More than one file was found with OS independent path 'blockExchangeProtos.proto'

So I guess you have to rename one of those files.

Also, you can test it yourself without compiling for Android with the commands in the readme.

[imsodin]

I guess that symlink solution was anyway more than a little bit dirty. Now I put the protos into the bep package and repository depends on bep - a little heavy handed but cleaner. I don't really see any other solution short of duplicating proto code. And repository can't be used for anything on its own anyway, right?

[Nutomic]

Yes that works. Thanks!