bar: floating panel is focused on mousedown instead of on mouseover (BC break in behavior) [Closes #269]

bar: fixed z-index issue when some panels are already in FLOAT mode when the page is loaded. [Closes #269]

- SPDX v3 screw up names of GPL licenses
- BSD-3-Clause is fully compatible with GPL

The context argument of an error handler is optional. Furthermore, it will be deprecated in PHP 7.2 (see http://www.php.net/manual/en/function.set-error-handler.php).