UI: Add a link to the GitHub commit at the bottom of the config screen

The "Go to GitHub commit for 30~41eb60d3" link at the bottom of the
configuration screen opens the URL solvespace@41eb60d3
and allows the user to see the date of the commit that SolveSpace was
built from.

Closes solvespace#1172

src/config.h.in

@@ -2,6 +2,7 @@
 #define SOLVESPACE_CONFIG_H
 
 #define PACKAGE_VERSION "@PROJECT_VERSION@~@solvespace_GIT_HASH@"
+#define GIT_HASH_URL "https://github.com/solvespace/solvespace/commit/@solvespace_GIT_HASH@"
 
 /* Non-OS X *nix only */
 #define UNIX_DATADIR "@CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_DATAROOTDIR@/solvespace"

src/confscreen.cpp

@@ -8,6 +8,7 @@
 #if defined(_OPENMP)
 #include <omp.h>
 #endif
+#include "config.h"
 
 void TextWindow::ScreenChangeColor(int link, uint32_t v) {
     SS.TW.ShowEditControlWithColorPicker(13, SS.modelColor[v]);
@@ -360,6 +361,8 @@ void TextWindow::ShowConfiguration() {
         Printf(false, " %FtOpenMP enabled");
         Printf(false, " %Ft   threads  %E%d", omp_get_max_threads());
     #endif
+
+    Printf(false, " %Fl%Ls%fGo to GitHub commit for %s%E", &ScreenGoToWebsite, PACKAGE_VERSION);
 }
 
 bool TextWindow::EditControlDoneForConfiguration(const std::string &s) {

src/textscreens.cpp

@@ -5,6 +5,7 @@
 // Copyright 2008-2013 Jonathan Westhues.
 //-----------------------------------------------------------------------------
 #include "solvespace.h"
+#include "config.h"
 
 //-----------------------------------------------------------------------------
 // A navigation bar that always appears at the top of the window, with a
@@ -90,7 +91,7 @@ void TextWindow::ScreenShowEditView(int link, uint32_t v) {
     SS.TW.GoToScreen(Screen::EDIT_VIEW);
 }
 void TextWindow::ScreenGoToWebsite(int link, uint32_t v) {
-    Platform::OpenInBrowser("http://solvespace.com/txtlink");
+    Platform::OpenInBrowser(GIT_HASH_URL);
 }
 void TextWindow::ShowListOfGroups() {
     const char *radioTrue  = " " RADIO_TRUE  " ",