dbuild tweaks

Some changes to the build so that it works well with dbuild.

- option to build aggregated play docs without caching the inputs (see: https://github.com/sbt/sbt/issues/1614)
- use the sbt settings for versions when writing the version file, so that dbuild can rewire settings
- make sure mima binary compatibility settings work well with dbuild
- fix the double cross versioning of run-support