Pulled implementation of iteration into superclass

This patch pulls the implementation of the actual iteration over the
objects to modify and the arguments into the superclass, which results
in less code in the subclasses.
Added missing argument
Fixed variable name
Fix: Added missing argument
Pulled help-string generation into class methods

To be more DRY, for CategorizeCommand classes
Pulled help-string generation into class methods

To be more DRY, for TagCommand classes
Merge branch 'refactor'