Merge pull request #70 from hynekcer/req

Direct SOQL aggregate queries + more
Implemented defer(..) and only(..) queryset methods
Enabled and improved tests for deferred fields queries
Tested the minimal number of queries for defer(..) and only(..)
Fixed configurable primary key name id/Id. added tests
Preserved order in get_classes_texts to improve reusability.
Fixing too many verbose names
bump for verbose_names