Turn off "show overlap" by default since scroll mode can replace it
in most cases where "show overlap" is used. And the dimmed area often
make new users confused. It's better to leave this feature to more
advanced users.
since the gesture detector will block the main thread
(the only thread in the lua part) for 300 ms on each tap
waiting for the arrival of the second tap, it makes the whole
application less responsive. 300 ms of latency is well perceived
in this case. This patch will simply disable double tap detection by
default as no widget now handles double_tap gestures. We could
temporarily enable double tap detection when this gesture is indeed
needed after.
