Improve "create association" gesture

[Cécile Camillieri]

When drawing a line between two classes, an association between the classes is created. The following improvements can be made to this gesture:

• The association should only be uni-directional, going from the first class to the class the gesture ended on.
• This gesture should work as well between classes and Implementation classes. In this case the association is always Class -> ImplementationClass.

[Matthias Schoettle]

Good idea! Btw: Does the mysterious bug still occur?

[Cécile Camillieri]

The one about the self association? It has been fixed. It happened when the view was zoomed in or out. Now we use containsPointGlobal to check the target point insted of getX() and getY().

[Cécile Camillieri]

Resolves #346, #353: association with unistroke gesture works with implementation classes and only creates unidirectional association. Association in the opposite directions not created anymore.

→ <<cset b73069b282ef>>