Replaced print by logging in backend
Never should be implemented raw aggregate count().

It is due to Django conventions about required 'id' field.
Fixed cursor for directly executed SOQL aggregate queries.
Implemented defer(..) and only(..) queryset methods
Enabled and improved tests for deferred fields queries
Tested the minimal number of queries for defer(..) and only(..)
Unused (maybe unuseful?) improvements of raw query.
Improved raw "select Count() from ", not fixed.
About directory structure
Renamed Test__c to django_Test__c.