Create simplified new child/relationship creation menu for UML Package diagram

[planger]

The new child / relationship creation menu should only contain the following UML concepts (equal to #7):

• [ ] Comment
• [ ] Model
• [ ] Package
• [ ] Containment Link
• [ ] Dependency
• [ ] Link
• [ ] PackageImport

[cdamus]

@planger I think there are some concepts missing from the list in this requirement:

• Constraint: sure, these can be complex, but even the most basic model needs to be able to specify constraints on the system that it describes
• Profile and Profile Application: if we can draw packages, we should be able to apply profiles. Without profiling, it will be difficult for users to customize the UML Light for their domains

Also, I think the Link item doesn't make sense: that's an instance-specification concept, which we've excluded from UML Light and wouldn't be in a package diagram, anyways.

Finally, I wonder since we have Package Import on the list, whether we shouldn't also have Element Import? It seems more basic than the Package Import. Although, the only element that could reasonably be imported in a package diagram is another package. But then again, the effect of an element import is quite different to a package import when importing a package ...

[cdamus]

Also, it's important to note that a bunch of things that are presented in other diagrams (classes, use cases, actors, behaviors) need to be in the New Child menu of a package, even though they cannot be visualized in a package diagram.

[cdamus]

In fact, I think it makes sense anyways to define just a single creation-menu model for each of the New Child and New Relationship menus covering all diagram types, which is what I have in progress now.

[cdamus]

Fixed with pull #22.