Update CSS and add restart warning

res/css/dark.css

@@ -1,5 +1,5 @@
 
-QWidget, QMainWindow, QMenuBar, QMenu, QDialog, QTabWidget, QTableView, QTableView::item, QScrollArea, QGroupBox, QPlainTextEdit, QLineEdit, QLabel
+QWidget, QMainWindow, QMenuBar, QMenu, QDialog, QTabWidget, QTableView, QTableView::item, QScrollArea, QGroupBox, QPlainTextEdit, QLineEdit, QLabel, MainWindow
 {
     background-color: #303335;
     color: #ffffff;

res/css/default.css

@@ -1,4 +1,4 @@
-QWidget, QMainWindow, QMenuBar, QMenu, QDialog, QTabWidget, QTableView, QTableView::item, QScrollArea, QGroupBox, QPlainTextEdit, QLineEdit, QLabel 
+QWidget, QMainWindow, QMenuBar, QMenu, QDialog, QTabWidget, QTableView, QTableView::item, QScrollArea, QGroupBox, QPlainTextEdit, QLineEdit, QLabel, MainWindow
 {
     /**/
     

res/css/light.css

@@ -1,4 +1,4 @@
-QWidget, QMainWindow, QMenuBar, QMenu, QDialog, QTabWidget, QTableView, QTableView::item, QScrollArea, QGroupBox, QWidget, QPlainTextEdit, QLineEdit, QLabel 
+QWidget, QMainWindow, QMenuBar, QMenu, QDialog, QTabWidget, QTableView, QTableView::item, QScrollArea, QGroupBox, QWidget, QPlainTextEdit, QLineEdit, QLabel, MainWindow 
 {
     background-color: #dadada;
     color: #000000;

src/mainwindow.cpp

@@ -505,7 +505,11 @@ void MainWindow::setupSettingsModal() {
         int theme_index = settings.comboBoxTheme->findText(Settings::getInstance()->get_theme_name(), Qt::MatchExactly);
         settings.comboBoxTheme->setCurrentIndex(theme_index);
 
-        QObject::connect(settings.comboBoxTheme, SIGNAL(currentIndexChanged(QString)), this, SLOT(slot_change_theme(QString)));
+        QObject::connect(settings.comboBoxTheme, &QComboBox::currentTextChanged, [=] (QString theme_name) {
+            this->slot_change_theme(theme_name);
+            // Tell the user to restart
+            QMessageBox::information(this, tr("Restart"), tr("Please restart ZecWallet to have the theme apply"), QMessageBox::Ok);
+        });
 
         // Save sent transactions
         settings.chkSaveTxs->setChecked(Settings::getInstance()->getSaveZtxs());
@@ -1627,11 +1631,6 @@ void MainWindow::updateLabels() {
 
 void MainWindow::slot_change_theme(const QString& theme_name)
 {
-    /*
-    QMessageBox msgBox;
-    msgBox.setText(theme_name);
-    msgBox.exec();
-    */
     Settings::getInstance()->set_theme_name(theme_name);
 
     // Include css