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
Demo version of koptreader config dialog.
add config options
first usable koptreader for new UI
make pdfreader and djvureader the defaults
larger option text in paperwhite
save/restore koptconfig to setting files
use koptinterface to reflow text in pdf/djvu readers