* 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.

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.