CHUI-689: When DND mode is enabled, making a direct delivery purchase results...

CHUI-689: When DND mode is enabled, making a direct delivery purchase results in an IM message from '(Nobody)'. Solution: Fixed a problem in process_improved_im that would falsy use system messages while in DND mode as an IM from a user. Also made it so that while in DND mode, SystemMessages and message with a high or greater priority are shown to the user as toasts (before a notification chiclet would just appear without the toast).