Implement the version schema described in T238.

Summary:
Implement the version schema and generate a version.properties file with the value 'version=<version string>.

The version schema depends on where we build.
  - Jenkins builds are named 1.4+b1024-r14c70ce6509
  - No jenkins build are named 1.4-SNAPSHOT

Test Plan:
Generate package with versions number on the form  1.4+b1024-r14c70ce6509
sbt -Dbuildnumber=10 clean stage dist

Verify with 'ls target/universal/*.zip'

Generate package with versions number on the form  1.4-SNAPSHOT
sbt clean stage dist

Verify with 'ls target/universal/*.zip'

Reviewers: martinp, borgem, kimtj

Reviewed By: kimtj

Differential Revision: https://phab.met.no/D117