Resolve "Use pointer-approach for UI to decrease compile time"

This MR changes the approach used for the Qt widget with Control from inheritance to "pointer-to-member", see https://doc.qt.io/qt-5/designer-using-a-ui-file.html#using-a-pointer-member-variable

This enables us to move the include for the automatically generated ui_control.h into the cpp file. Of course this means that no one beside Control knows the widgets which are part of control. Therefore it is necessary to make all accesses to the ui part of Control itself and let any other class only interact to the ui through public methods of control. This migration of all code which uses the ui into the Control-Class is part of this MR as well. (With the exception of the trackShowOnlyNrList, which is a bit more involved)

Closes #187 (closed)