Provide a new way to create goal

[Romain Alexandre]

1) Drawing a line from Goal to Empty Space that will create an outgoing (based on the "from" goal) contribution and a goal at the same time (vs two gestures to achieve the same)

It can not be used for the root goal. The root goal can not have an outgoing contribution.

2) Drawing a line from empty space to goal that will create a goal and an incoming (based on the "to" goal) contribution at the same time.

Warning : Right now, when you want to create a contribution we check that the start position of your UnistrokeEvent is close to an impact model element (20 px). So for this second point, it can be a problem if the user click a little too far (21px for example), it will create a new goal.