Signature data is not updated if mouse-up happens out of canvas.

[saurabh-jtg]

• If user starts signing and goes out of canvas, the signature data is not updated which may be confusing for user.
• The reason is that touchEnd event is not fired within the directive which triggers the update (updateModel() method).
• One way to handle this is by also updating the signature data when user goes out of the canvas using focus-out.

[paolosanchi]

it should be a duplicate of this:
#44