applets/taskmanager: Open context menu on press, not on click
TapHandler suck, it can't be used for onPressed signal, because when menu takes over the input grab, the handler won't clear/cancel its grab. It results in subsequent presses and taps failing to register, i.e. the component becomes non-functional, until some other Tap or other Handler is activated in the same Quick scene (i.e. Plasma panel in most cases).
…and a bit of other porting/refactoring.