Adds real support for ToolTips.

This patch changes the Event drawing so it
can display tooltips. It is now responsability
of the item to show / hide a tooltip.

A bit of code-refactoring got on here too
because I was using only QGraphicsItem calls
and I wanted to use a hover in / hover out event
to show / hide the tooltip.

Signed-off-by: Tomaz Canabrava <tcanabrava@kde.org>
Added a bit of documentation on how to use the ToolTips & removed 2 bad-api methods

Signed-off-by: Tomaz Canabrava <tcanabrava@kde.org>