This commit ensures we correctly detect and import
Data*Associations and Associations.
It aligns logging across the import components, too, being slightly more
verbose and helpful.
Related to #112
This commit ensures we pipe invisible root elements (Process,
Collaboration) through our import infrastructure, too.
This way we we receive proper events for them.
Related to #6
Instead of failing hard when we parse invalid flow elements (i.e.
TextAnnotation) we log a warning that may be handled by the diagram
import.
Related to #74
