add swipe event detection in gesturedetector.lua
use swipe gestures in menu widget to signal page turn
bug fix for swipe gesture detection (nil x or y)

a complete_last_ev var is used to make sure the first argument
to isSwipe() method has no nil x or y entry.
use left swipe for next page turn
correctly report timeout on select timeout
Merge pull request #682 from houqp/swipe

Swipe gesture support