D-2

v-2.1
---
1. action down => draw a circle
2. touch on a point in the screen
	=> the circle gets drawn on the point;
	=> the previous one gets deleted

	==> done
D-2

v-2.2
---
1. move circle
	    => according to the distance moved
	    => not according to the move value

	==> done
Merge branch 'D-2_use-canvas'