Handle the -batch option centrally in cmdline.c.

This removes one case from several of the individual tools'
command-line parsers, and moves it into a central place where it will
automatically be supported by any tool containing console.c.

In order to make that not cause a link failure, there's now a
stubs/no-console.c which GUI clients of cmdline.c must include.

stubs/no-console.c

@@ -0,0 +1,10 @@
+/*
+ * Stub functions for when console.c is not linked into a program.
+ */
+
+#include "putty.h"
+
+bool console_set_batch_mode(bool newvalue)
+{
+    return false;
+}