Drag multiple shapes together

[thomaspeugeot]

Steps:

• #48
• #49

[thomaspeugeot]

2 problems:

• when the dragging cursor starts, the movement of the shape is immediatly 20px to the top. Probably a bad calculation of pageY.
• when the dragging cursor escapes the shape, there are awkward behaviors.
• when the cursor is above another shape, dragging stops