Improve Modelers functions related to Specialization

The concept of inheritance is very powerful and often useful. It is implemented in Mendix by means of Generalization and Specialization

1. Give the Listview a better way to manage the templates per specialization:
   1. At template creation, give the option to select the attributes that need to get shown, as alternative to filling the template with every attribute.
   2. Have the option to select some snippet
   3. Make the presence of specializations more visible by replacing the text "Default template (1 of 2)" by also showing the names of the other template. Similar to how tabs are shown.
2. Make it possible to inherit the access rights from the generalization.
3. Give Dataview the same template options as the Listview.
4. Make the connection between the entities more obvious in the domain model, maybe by adding lines from generalization to specialization 1 - 1
5. Create the option to specialize existing general objects. Currently that is hardly possible and you need to have your domain model setup up front.