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 puts all import related stuff into the import module.
The core module remains as an entry point to require the basic modules
needed by bpmn-js. At the time this is { import, draw }.
jdotzki
Nico Rehwaldt