Create separate icon theme for Mac OS X.

In code we rely on icon themes. On linux systems there is a standard that describes such a icon theme. This gives users same look for all applications those support icon themes. Different situation on Windows and Mac. For Windows we mimic for Valentina this behavior bringing in resources Windows icon theme. Because we don't have separate theme for Mac OS Valentina uses the theme for Windows. These days we have possibility to improve our support for Mac and make our Mac users even happier. Giving them native icons one small step to this.