Add option to control CSRF protection

Some users are using WebUI with simple port-forwarding from their router,
providing an option to control the protection will save them from setting up an
non-trival web proxy.
Closes #7274.

src/webui/webapplication.h

@@ -145,4 +145,5 @@ private:
 
     // security related
     bool m_isClickjackingProtectionEnabled;
+    bool m_isCSRFProtectionEnabled;
 };