add haptic feedback to task switcher gestures

adds haptic feedback when activating task scrub mode and the first time the conditions are met for the task switcher to open (since the user can then move the finger in a way to make it not trigger anymore we don't want the ability to make the haptics go crazy so it is only allowed to trigger once per invocation of the gesture. this is in line with the haptics behavior on my android, but I'm open to feedback if people wanna do things differently)

fixes #366 (closed)