On Linux and Mac OS, this action brings the LyX window into focus.
Such behavior is not allowed by Windows OS so instead the color of
the taskbar entry is changed to indicate that the window has changed
in some way.
The action is hidden in the shortcuts menu because it would make
sense to assign a shortcut to it. The only way to execute shortcut
would be if the LyX window is already activated.
lyx-activate will be used (see next commit) to allow the PDF viewer
to switch to LyX after executing a reverse search.
60515b996b