Refactored all scripts so that they are divided into a `prepare`
and a `publish` phase. By this we can build, test, tag, commit
everything first. Only if all of this is ok we start pushing
to Github. By this we keep Github consistent even in error cases.

Extracted include script `/scripts/utils.inc`:
- parse and validate named arguments in the style
  `--name=value`
- proxy git command and deactivate `git push` based on
  command option `--git_push_dry_run=true`
  (will be inherited to child scripts)
- enable/disable bash debug mode by command option
  `--verbose=true`
- dispatch to functions based on command option
  `--action=...`
- helper functions for dealing with json files