Consistent versioning: Git/GitHub vs. Sbt vs. Hardcoded

[mschwerhoff]

Git/GitHub and Sbt version are currently out of sync. For example, release v.21.01 is tagged as v.21.01-release, but it's Sbt version is still 0.1-SNAPSHOT.

Silicon uses a combination of Sbt version and git revision to identify itself, e.g. as Silicon 1.1-SNAPSHOT (ebd845cd). Carbon uses neither, and reports a hardcoded version, e.g. carbon 1.0.

At least for official releases, all (publicly visible) versions should be in sync.