device: clear some confusion about gestures

rename the "Knock On Gestures" category to "Gestures"
add a summary what it is actually doing

Change-Id: I9769e2c459d2b80405e11c5382a73a3b45e38ebd
fix the actionbar at the flasher fragment

Change-Id: I7f6fd5f1295a132f0f8a2af778b0cee2d05880b0