Generate more information about extended and used classes

[MartinMalinda]

Needed for ember-learn/ember-api-docs#243.
Temporary solution merged here ember-learn/ember-api-docs#248

At this point, properties like extendedClassProjectName and extendedClassVersion are computed properties. Ideally, this would be generated here - it would be more clean and error proof.

https://github.com/ember-learn/ember-api-docs/pull/248/files#diff-672353df31213c934c7ea38ccb99b7deR54