Added overview toggle to allow for button-based overview toggling

Added add/removeEvents methods to allow for adding& removing event
listeners that may interfere with other libs.

added left, right, up, down gestures to change slides. moved window edge slide triggers to a touchend event to prevent interference of gestures

hjkl for directions.
space to move to next slide.
esc for 3D overview (instead of space)

change back state event scope, document level makes more sense as that's where the state class is applied

Firing custom event based on data-state name. This allows developers to trigger custom javascript code on a per slide basis.