Revise WidgetToolTipTest.js
Move tooltip text configuration to WidgetToolTip.js
Add test for tooltip positioning relative to mouse
Position tooltips for toolitems below the item
Set tooltip text in show method

Fixes Bug 375850 - ToolTip can change content while fading out
Merge PopupAtom.js into ToolTip.js
Use MultiCellWidget to render tooltip text
Start tooltip hide timer only after mouse exits widget
Prevent flickering when re-positioning the tooltip
Make WidgetToolTip extend Popup directly

This allows changing internals without worrying about GridCellToolTip.
All three (base.ToolTip, WidgetToolTip, and GridCellToolTip) may be
merged later.
Implement customizable tooltip delays
Skip tooltip appear timer if it is already visible
Support tooltip to appear only if mouse rests
Support tooltip disappear on mouse move
Position tooltip on top of a widget if there is more space

Actually if there is more space at the top than one third of the space
at the bottom
Restrict tooltip bounds to page
Support tooltips positioned vertically centered to widget left or right
Skip tooltip timer and animation when moving fast between widgets
Support left aligned tooltips
Move gridCellToolTip related code from Grid.js to GridCellToolTip.js