WebAPI/Softkey through context menu

Idea

Relevant bugs: bug 1142855 (meta)

On simple phone, there are several (two, usually) softkeys on the screen. Sometimes a drop menu will show when clicking one of them. The functionality and caption of these softkeys may vary under different apps but should have the same look across the system. We may need an interface which can let each app easily customize their own softkeys without being aware of how they are rendered.