SBT: expose current build version via BuildInfo (#2913)
SBT: expose current build version via BuildInfo (#2913)

Also, move protobuf files into a subdirectory since that plugin tends
to delete its target directory and thus affects other code generators.
scalameta/scalameta,scalameta/scalameta,scalameta/scalameta,scalameta/scalameta,scalameta/scalameta