Support SNAPSHOTs.

[cgruber]

Note - this could be an "at the time of workspace evaluation" resolution, or it could involve pinned versions. Either way, the repository structure file system structure of http://some.repo.root/maven/com/google/dagger/2.20/dagger-2.20.jar doesn't work for snapshots, which are, for the standard "HEAD-SNAPSHOT" version dagger uses, more like: https://oss.sonatype.org/content/repositories/snapshots/com/google/dagger/dagger/HEAD-SNAPSHOT/dagger-HEAD-20190108.194818-169.jar

So this would need to either have pinned versions declared, and then test for the "${version}-${date}.${integer1}-${integer2} version pattern and go into the "${version}-SNAPSHOT" folder to fetch it, or it would need to test for "-SNAPSHOT" and pull the maven-metadata.xml file, grab the snapshot details, and construct the path that way.