Delay showing tooltips, dont let them follow the pointer once shown.

Add user defined tooltips for itemimagebutton.
This most likely will not cause a delay of 400 ms in following situation:
1) mouse over element  --> hovered != NULL
2) mouse leave element --> hovered == NULL
3) mouse over same element --> tooltip shown immediatly

For what I remember game buttons in sigleplayer are surrounded by hovered == 0 guess you could check the behaviour there.