pass color_group to backend.event()
make impl/modules a sub package
remove stale test database files
devserver sets up basic logging config
extract model classes into separate modules
extract basic operation subclasses
extract Operation.subclass_for
add as_dict/to_dict alias
add dummy-operation subclass
add comment about query performance
fix code to eliminate performance warning
rename dummy-operation to pass-through
use '{in,out}put connector' to identify connectors