Improve sqlalchemy filter rules

Improve sqlalchemy filter rules

Thanks to Elrond's review. 1) Use filter_by more consistently
rather than mixing filter and filter_by. 2) Add multiple AND
conditions in the same filter rule rather than using separate
ones. 3) The atom feeds used filter_by(Modelname.attr == ...)
which was the wrong pattern, of course.

Thanks for repairing my junk Elrond!

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>