Add basic cross-signing support

(cherry picked from commit e1795076c8c41a34b91c31df35d1e344d0b14887)

src/controller.cpp

@@ -417,3 +417,12 @@ bool Controller::ssssSupported() const
     return false;
 #endif
 }
+
+bool Controller::csSupported() const
+{
+#if Quotient_VERSION_MINOR > 9
+    return true;
+#else
+    return false;
+#endif
+}