feat(attribute_directives): tooltip demo and popover exercise

@IgorMinar new demo + exercise, this time to illustrate attribute directives that do good, old DOM manipulation. Actually those little examples illustrate many important concepts:
* factory function vs. compile function vs. linking function
* observing iterpolated attributes
* place of jQuery (low-level DOM manipulation and DOM-based testing)

so I think it might be good idea to start with exercise. We could then nicely transition to widgets and say: "hey, we can do old-fashioned DOM manipulation in directives but it is often not needed as directives with templates can be seen as mini applications " .