Simplify release branching as much as possible

Now the release-helper.sh script has a single action
branch-release that can be used to do everything related
to normal release branching except pushing the changes to
origin.

Also the action bump-master-version simplifies the version
bumping done for platform and simupedia master branches
after a release is branched.

gitlab #71

Change-Id: I71d7936a610b2f3a5228405680779bb3ae2e2ed7