Add -version option to get just the version

Adds a `-version` or `--version` option to print just the version
of the program for bitcoind, bitcoin-cli and bitcoin-qt.

Also make it that `-help` can be used to display the help (as well as
existing `--help`). Up to now, `-help` was the only option that didn't
work with either one or two dashes.

src/qt/bitcoin.cpp

@@ -503,9 +503,9 @@ int main(int argc, char *argv[])
 
     // Show help message immediately after parsing command-line options (for "-lang") and setting locale,
     // but before showing splash screen.
-    if (mapArgs.count("-?") || mapArgs.count("--help"))
+    if (mapArgs.count("-?") || mapArgs.count("-help") || mapArgs.count("-version"))
     {
-        HelpMessageDialog help(NULL);
+        HelpMessageDialog help(NULL, mapArgs.count("-version"));
         help.showOrPrint();
         return 1;
     }