[Qt] massive options/settings rework (no core changes)

- add new options for database cache and script verification threads
- add label which displays options that are overridden by command-line
  parameters
- proxy settings are not applied on-the-fly anymore and require a client
  restart (ApplyProxySettings() was removed and was not working very well
  anyway)
- re-work options reset and require a client shutdown (as it is much
  easier to do it this way without having to mess with what can be changed
  on-the-fly and what needs a restart anyway)
- options reset now writes default values for every single option
- when changing an option which requires a client restart display a 10
  second warning message in statusLabel (via a QTimer)
- when applying the changes via ok change that to a persistent message,
  which is displayed even after closing optionsdialog and re-open it, when
  no client restart was made
- remove dialog boxes used when changing language or proxy settings
- add setRestartRequired() and isRestartRequired() to OptionsModel and
  use the set function when updating options to signal OptionsDialog
  when a restart is needed
- resize optionsdialog a little and add some min sizes for certain GUI
  elements
- remove apply button from optionsdialog
- save and restore optionsdialog window position
- update nTransactionFee in QSettings with a set -paytxfee value when
  opening optionsdialog (I'm not sure about this yet, perhaps revert to
  not updating QSettings and just display current -paytxfee value in
  optionsdialog.)

src/qt/optionsdialog.h

@@ -31,35 +31,28 @@ protected:
     bool eventFilter(QObject *object, QEvent *event);
 
 private slots:
-    /* enable only apply button */
-    void enableApplyButton();
-    /* disable only apply button */
-    void disableApplyButton();
-    /* enable apply button and OK button */
-    void enableSaveButtons();
-    /* disable apply button and OK button */
-    void disableSaveButtons();
-    /* set apply button and OK button state (enabled / disabled) */
-    void setSaveButtonState(bool fState);
+    /* enable OK button */
+    void enableOkButton();
+    /* disable OK button */
+    void disableOkButton();
+    /* set OK button state (enabled / disabled) */
+    void setOkButtonState(bool fState);
     void on_resetButton_clicked();
     void on_okButton_clicked();
     void on_cancelButton_clicked();
-    void on_applyButton_clicked();
 
-    void showRestartWarning_Proxy();
-    void showRestartWarning_Lang();
+    void showRestartWarning(bool fPersistent = false);
+    void clearStatusLabel();
     void updateDisplayUnit();
-    void handleProxyIpValid(QValidatedLineEdit *object, bool fState);
+    void doProxyIpChecks(QValidatedLineEdit *pUiProxyIp, int nProxyPort);
 
 signals:
-    void proxyIpValid(QValidatedLineEdit *object, bool fValid);
+    void proxyIpChecks(QValidatedLineEdit *pUiProxyIp, int nProxyPort);
 
 private:
     Ui::OptionsDialog *ui;
     OptionsModel *model;
     MonitoredDataMapper *mapper;
-    bool fRestartWarningDisplayed_Proxy;
-    bool fRestartWarningDisplayed_Lang;
     bool fProxyIpValid;
 };