Theme support for tool windows

Windows has this concept of 'tool windows' which essentially creates an always-on-top window with a more compact, limited titlebar.

This is toggleable in Qt using the Qt::Tool flag, however AeroThemePlasma doesn't seem to replicate this behavior so far.

A test of this is eg. my ribbon fork of Kolourpaint where the floating palette window that has the Qt::Tool flag is displayed with a normal titlebar.