Refactor: Move Semver from slice3r to libslic3r

A static symbol Slic3r::SEMVER is introduced, which holds
the running slicer's Semver object.

This is mainly done to make testing updater behaviour
_much_ easier. Additionaly to cleanup some questionable code
(Semver was being parsed multiple times / in multiple places
in the frontend.)

src/slic3r/Config/Version.hpp

@@ -7,7 +7,7 @@
 #include <boost/filesystem.hpp>
 
 #include "libslic3r/FileParserError.hpp"
-#include "../Utils/Semver.hpp"
+#include "libslic3r/Semver.hpp"
 
 namespace Slic3r { 
 namespace GUI {