Pin Edit/Save button to lower end of Detail Panel
Especially with large entry forms (complex composites with many entry fields) it is unsatisfactory having to scroll all the way to the end of the form to click the Save button. It would be easier to find the Edit/Save button always at the same location at the bottom of the Detail Panel.
This is a follow-up of dmx-intern/feature-planing#46
Also related to #73 (closed)