RuntimeTabMenu should allow a user to change the type of a graph provider and provide better list support

[koschke]

The addition and removal of list elements is rudementary currently. We can add only at end of a list and remove only the last element of a list. A user may want to add or remove an element anywhere. A user may even want to change the order of the list elements. This is needed for all lists where the order matters. The order matters, for instance, in graph-provider pipelines.

If a list contains instances of different classes (deriving from the same class), a user needs to specify the type of a list element. Again, that is needed in graph-provider pipelines where we can have all sorts of graph providers (e.g., GXL, CSV, JaCoCo, etc.).