optionsdialog cleanup

- remove duplicate includes, that are already present in ui_optionsdialog.h
- change QIntValidator to not allow 0 as port-number
- re-order some function calls to match the Ui element order, for better readbility and to prepare for the addition of further IPv6 and Tor proxy options
- restat warning for the language selection is only shown, when the language was changed (not on simply activating the Ui element)
- split check for object == ui->proxyIp into seperate if-clause
- micro-optimize the code in the above mentioned if-clause
- unify used format for comments in the code
- introduce handleProxyIpValid() function, which handles UI elements and the
save button states for valid/invalid proxy IPs

src/qt/optionsdialog.h

@@ -8,6 +8,7 @@ class OptionsDialog;
 }
 class OptionsModel;
 class MonitoredDataMapper;
+class QValidatedLineEdit;
 
 /** Preferences dialog. */
 class OptionsDialog : public QDialog
@@ -38,9 +39,10 @@ private slots:
     void showRestartWarning_Proxy();
     void showRestartWarning_Lang();
     void updateDisplayUnit();
+    void handleProxyIpValid(QValidatedLineEdit *object, bool fState);
 
 signals:
-    void proxyIpValid(bool fValid);
+    void proxyIpValid(QValidatedLineEdit *object, bool fValid);
 
 private:
     Ui::OptionsDialog *ui;