Fixed tests for incomplete test project directories after switching git branches
Fixed some comments and messages
Fixed the demo homepage to work also with a normal Account.

It should also never raise exception for any user input.
Fixed __repr__ for query to be more exact, though less intuitive.
Removed RoutedModelAdmin as not important, replaced by an empty stub.

RoutedModelAdmin only explicitely discovered the database name by calling
database routers configured in "settings.DATABASE_ROUTERS". That is the same
what is otherwise arranged implicitely a few later by Django.
Removed RoutedModelAdmin also from the demo application.
Moved "reauthenticate" from backend.query to auth module.
Configured coverage with a more clear filename.
Implemented defer(..) and only(..) queryset methods.

Output fields can be specified by also in some internal methods.
Enabled and improved tests for deferred fields queries.
Tested the minimal number of queries for defer(..) and only(..)
Added settings SF_PK for configurable primary key name: 'Id' or 'id'.

The similar undocumented feature for individually configurable names sf_pk
by models has been removed.
Implemented multiple inheritance of database Model from more abstract models.
Fixed SalesforceModel for proxy models.
Added tests for multiple inheritance (abstract models, proxy, mixins).
Fixed unimportant inconsistent spaces/tabs in Python code etc.
Merge pull request #78 from hynekcer/multiple-inheritance

Multiple inheritance