Allow task separation through release.properties

[mp911de]

We should introduce means of controlling what targets should be run by the automated release tooling, ideally through release.properties as this is a place that needs to be edited for a given release.

We have three scenarios:

1. Run the full release (full)
2. Prepare the release and push tags (tag)
3. (Re-)run binary and documentation builds including staging. This step requires release tags to be present (build)

The full target is composed from tag and build targets. That separation allows for retries.

[gregturn]

This mechanism should allow, through Jenkins' ability to read properties files, to conditionally run different phases of the build.