Refactoring some controls

[edan-bainglass]

It is often that controls come in packs, e.g. axes limits, down-selection, etc. Even in the case of a single control, it is not only adding the control to the view, but also "plugging" it in to the plot presenter, i.e. observing/reacting to it. It would greatly reduce burden on current classes if these single/grouped control features could be refactored into Control(s) classes to be dropped in where desired.

Initial attempts to implement these ran into the infamous inheritance diamond problem. The Mixin pattern was also considered but not yet attempted. More thought is needed on this matter.

Input welcomed!