The rationale of this pull request is to
* have more maintainable and granular code
* not maintain the custom made job engine
* allow the users to customize the defaults of the releaser more easy
* allow the users to create their own steps without the need to change any existing code
* allow the users to fully change the flows and tasks logic
* abstract underlying batch mechanism (Spring Batch) so it doesn't leak to production code
* allow parallelization of the release process and release tasks
