PEP 8 cleanups
Default for GenericForeignKey()'s fk_field is object_id
Triggers and SQL beautified
Avoid duplicated actions in the triggers
Let the user decide what keyword arguments are passed to the denormalized field (no magic involved)
Denorm function could return either an object or a PK

Without this, foreign key fields (like 'some_id') could end up
having objects instead of IDs.
Using quote_name for all field names.

Some fields need this (particularly those with lower and upper case
or those that otherwise would be reserved keywords).

Along the way, connection's using 'using' was normalized to be
consistently used and passed around where it was needed.
Added support for swapped models