no content assist in freemarker templates for interface-based beans

If your beans in freemarker templates are described by an interface, the code completion (content assist) will not work.
There two mechanism implemented to provide content suggestion:

1. Bean-Introspection: this doesn't work for interfaces
2. Java Reflections: there are bugs which prevent any suggestions

My suggestion: use only reflections - it will work for both and isn't that harder to implement.
I'm working on a pull request for fixing this issue.