Use separate ToolTipDelegates for open windows and pinned apps in Task Manager

Instead of sharing a ToolTipDelegate for all the task manager items and changing mainItem and resizing as needed, share one ToolTipDelegate for all open windows and one for all pinned apps for them.

Advantages:

• Smoother animations
• Tooltips are not wrongly positioned when switching from unopened pinned app to open app entry
  • We can remove the hack in !383 (merged)
• Fixes Bug 434657

Explanation:

• Having a single shared ToolTipDelegate causes problems with Dialog positioning when the size changes significantly. Since we share them only for those tooltips which are the same in size, this doesn't occur.
• If a ToolTip's internal ToolTipDialog is dismissed by a LeaveEvent, opening the same tooltip (different content) in another location will have to move the tooltip to the new location, and in this interval another LeaveEvent is fired, causing the new tooltip to close immediately.