Added SystemInfo dialog,

a new SLIC3R_BUILD define to be replaced by the build script,
a menu item to open the "New Issue" github page.

xs/src/libslic3r/libslic3r.h

@@ -15,6 +15,7 @@
 
 #define SLIC3R_FORK_NAME "Slic3r Prusa Edition"
 #define SLIC3R_VERSION "1.31.6"
+#define SLIC3R_BUILD "UNKNOWN"
 
 //FIXME This epsilon value is used for many non-related purposes:
 // For a threshold of a squared Euclidean distance,

xs/xsp/XS.xsp

@@ -17,6 +17,12 @@ VERSION()
         RETVAL = newSVpv(SLIC3R_VERSION, 0);
     OUTPUT: RETVAL
 
+SV*
+BUILD()
+    CODE:
+        RETVAL = newSVpv(SLIC3R_BUILD, 0);
+    OUTPUT: RETVAL
+
 SV*
 DEBUG_OUT_PATH_PREFIX()
     CODE: