Fix touchscreen behaviour for taskbarAppIcon (#223)

[moqmar]

Behaviour that might be unexpected:

• long-pressing a background application opens the popup menu, but still activates/starts the application. Only activating the application on TOUCH_END/TOUCH_CANCEL turned out to work only sometimes on my system, I'll do some further tests on that.
• dragging via touchscreen is completely disabled for now, as it gets confused with the mouse, bugs around and in the end breaks everything (as said in the issue, up to a frozen system).

[moqmar]

Alright, turns out that the TOUCH_END/TOUCH_CANCEL events only fire sometimes, for completely unknown reasons, although I don't know why the popup doesn't open in those cases... :/

[moqmar]

Ah, it doesn't open because a leave event is fired instead. So, the fix now behaves as expected.

[jderose9]

Great, thank you!!