Redesign update service

[swagner]

It turned out that the update service of HeuristicLab 3.3.x has some drawbacks:

• The plugin infrastructure itself cannot be updated. If the plugin infrastructure has to be changed, updating HeuristicLab plugins with the update service will result in an inconsistent state.
• The update service cannot update the application configuration. Therefore it is not possible to add/update the definition of services which are used in plugins (e.g. OKB, Hive).
• Grouping plugins to products is not really useful and was never effectively used in HeuristicLab 3.3.x.
• Working with the plugin administration UI is quite cumbersome. The usability should be improved.

Therefore we should think about a fundamental redesign of the update service for HeuristicLab 3.4.x.