Tooltips > Add a delay to display them

Tooltips are useful but we don't want to disturb user by displaying them at each rollover if he doesn't need it.
In the other hand, tooltips have to be displayed quickly to be seen.

What we can do:
1/ tooltips are displayed with a ~ 0.2s delay
2/ if you rollover another tooltiped element in less than 2sec, the tooltip is displayed without any delay
3/ if you don't hover element in 2 sec, you go back to step 1.