UML-280: Unsynchronize Package Hierachy diagram

Unsynchronize diagram
Add mapping for model
Add Existing Elements with :
 * Add tool
 * Remove tool
Add merge creation tool and reconnect merge tool
Review Usage label
Add drop tool to drop package from model explorer to diagram
Add related tool
UML-280: Package Containment Diagram

This diagram show the package contents as list. It is possible to
drag & drog elements from one package to another from the model
explorer vview or from another package in the diagram.
This diagram also defines an optional layer that shows the components
and list all the elements contained.
UML-280: Package Containment diagram in Travel Agency

Add a Package Containment diagram in the Travel Agency example
and reorganize the model to create packages