Added custom Gesture detectors

-Moved the Scale Gesture detector in the Activity.
-Implemented Rotation and translation callbacks.
-The events are handled in the activity, not the view itself : if the
view handles the gestures itself, each time it moves, it detects an
inverse dx,dy, causing another move (especially in rotation case).
Also, it allows to use the whole space, not just the view to detect
these gestures.