Merge "Contexts" and "Next Actions" into one tab

Frankly I don't see why "Next actions" and "Contexts" are not one single tab. All the tiny icons for manipulating stuff in the "Contexts" tab, might just as well have been put in front of/after the headlines in the "Next Actions" tab.

If there also was a "minimize all" link/button one could just as easily manipulate the headlines directly.