Keep the BalloonTip open when the BalloonTip's arrow prevents the cursor
from being inside the spawning ToolTipWidget, which triggers the
ToolTipWidget's leaveEvent and would previously close the BalloonTip.

When that happens track the cursor until it either leaves the
ToolTipWidget's bounding box or leaves the BalloonTip and goes back to
the ToolTipWidget, and respectively close the BalloonTip or leave it
open.

* Fix irregularly shaped corners
* Remove extra space for BalloonTips with no message or no title
* When the target tip location is not on a screen, put the tooltip on
  the mouse's screen instead of the primary screen
* Fix description getting cut off when the title was too long
* Expose border width as a parameter
* Fix spacing and sizing issues with larger border widths

This makes it so that if you just want to reload the current style (eg. on program start, or in response to a system event), you don't need to know the name of the currently selected user style. It's also more consistent with the way the 'userstyle/enabled' flag works.

BalloonTip.h/cpp are only used from the ToolTipControls folder, so move
them there.

fixes balloon remaining onscreen when parent gets
hidden via escape key for example.