Bean Generator improvements

The following improvements for the bean generator tool have been identified:

• Add "TODO" comment to beans if the generator could not generate a (complex) function.
• Check if taggable document types, i.e. document types that get installed with the hippostd:taggable mixin, get installed with the getTags() function already in place.
• Allow more selectiveness for (re-)generating beans
• Provide a preview of the to-be-added/removed methods
• Provide feedback of the added/removed methods