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/libslic3r/libslic3r.h

@@ -19,6 +19,7 @@
 #include <cmath>
 
 #include "Technologies.hpp"
+#include "Semver.hpp"
 
 typedef int32_t coord_t;
 typedef double  coordf_t;
@@ -92,6 +93,8 @@ inline std::string debug_out_path(const char *name, ...)
 
 namespace Slic3r {
 
+extern Semver SEMVER;
+
 template<typename T, typename Q>
 inline T unscale(Q v) { return T(v) * T(SCALING_FACTOR); }