Generate version header when configuring project

The basic idea is we create a version header template at
"src/base/version.h.in" and the build systems are expected to replace
strings that are enclosed with @ symbols and generate
"src/base/version.h" for other source files to consume/include.

src/gui/mainwindow.cpp

@@ -70,6 +70,7 @@
 #include "base/utils/fs.h"
 #include "base/utils/misc.h"
 #include "base/utils/password.h"
+#include "base/version.h"
 #include "aboutdialog.h"
 #include "addnewtorrentdialog.h"
 #include "autoexpandabledialog.h"