Allows direct computation of the version based on versioning information

[dcoraboeuf]

A project version can be somehow very complex, based on different strategies. The versioning plugin was very opiniated about this.

In many circumstances, we want just want to compute the version based on SCM version.

Goal of this feature is to allow a construct like this:

versioning {
   version = { scmInfo, versionInfo -> // compute version based on provided elements)
}

allprojects {
   version = versioning.version
}

The versionFile will also inject the Gradle version as VERSION in the version.properties file.