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(..)
Unused (maybe unuseful?) improvements of raw query.
Improved raw "select Count() from ", not fixed.
About directory structure
Renamed Test__c to django_Test__c.
Fixed comment
Use OrderedDict for directly executed custom SOQL; TODO tests or special class