Refactor database object methods to reduce duplicate code

[Dantali0n]

Many of the database objects methods share a lot of code that could potentially be reduced.

    def find(session, reference, allow_multiple=True):
        reference._build_object()

        """Only look for serial devices"""
        reference.m_device.interface = DeviceInterfaces.SERIAL

        base_filters = reference._filter(reference.m_device)

        """Check if reference is base or child type when setting filters"""
        if hasattr(reference, 'm_serial_device'):
            filters = reference._filter(reference.m_serial_device)
        else:
            filters = {}

        query = session.query(Device).filter_by(**base_filters)\
            .join(SerialDevice).filter_by(**filters)

    def delete(session, reference, allow_multiple=False):
        reference._build_object()

        filters = reference._filter(reference.m_device)
        query = session.query(Device).filter_by(**filters)