Add CSS/JS static files for material select2

The static files used to materialize select2 fields should be available in the core so that they can be accessed across the whole project.

changed milestone to %2.0a2

added part::frontend label

created merge request !218 (closed) to address this issue

mentioned in merge request !218 (closed)

created merge request !219 (merged) to address this issue

mentioned in merge request !219 (merged)

mentioned in commit 144435d6

closed via merge request !219 (merged)