st-button: Ignore pointer emulated touch events
In X11, pointer emulated touch events are replicated with normal PRESS, RELEASE pair events which are generated by the server. Thus for a single tap we get:
- TOUCH_BEGIN -> TOUCH_END, PRESS -> RELEASE
This will cause st-button to send two "clicked" signals, instead of just one, breaking extensions (like dash-to-dock) that show buttons in the main stage which will be checked two times or that will receive the same signal two times.