isValidDrag should ignore "tap" events

detect ̀ ``touchmove``` instead of `̀``touchstart``` event. This way we ignore simple "taps" on screen, meant to use links, etc...


This is similar to #104 but I didn't merged them as i'm not sure of the way I should use touch events. However, I'm pretty much sure touchmove is the way to go to be able to use link while drag&drop is activated.