[libcalamares] Add a reload-stylesheet button

- This is a debugging-option to test stylesheet changes quickly.
 - Right now, the stylesheet is cached, so it doesn't even work.

src/calamares/CalamaresWindow.cpp

@@ -59,7 +59,7 @@ CalamaresWindow::CalamaresWindow( QWidget* parent )
     // If we can never cancel, don't show the window-close button
     if ( Calamares::Settings::instance()->disableCancel() )
         setWindowFlag( Qt::WindowCloseButtonHint, false );
-        
+
     CALAMARES_RETRANSLATE(
         setWindowTitle( Calamares::Settings::instance()->isSetupMode()
                             ? tr( "%1 Setup Program" ).arg( *Calamares::Branding::ProductName )
@@ -74,6 +74,7 @@ CalamaresWindow::CalamaresWindow( QWidget* parent )
     using CalamaresUtils::windowPreferredHeight;
     using CalamaresUtils::windowPreferredWidth;
 
+    // Needs to match what's checked in DebugWindow
     this->setObjectName("mainApp");
 
     QSize availableSize = qApp->desktop()->availableGeometry( this ).size();
@@ -173,7 +174,7 @@ CalamaresWindow::CalamaresWindow( QWidget* parent )
     //       and requires an extra show() (at least with KWin/X11) which
     //       is too annoying. Instead, leave it up to ignoring-the-quit-
     //       event, which is also the ViewManager's responsibility.
-    
+
     mainLayout->addWidget( m_viewManager->centralWidget() );
     setStyleSheet( Calamares::Branding::instance()->stylesheet() );
 }

src/libcalamaresui/utils/DebugWindow.cpp

@@ -20,8 +20,10 @@
 #include "DebugWindow.h"
 #include "ui_DebugWindow.h"
 
+#include "Branding.h"
 #include "utils/Retranslator.h"
 #include "utils/qjsonmodel.h"
+
 #include "JobQueue.h"
 #include "Job.h"
 #include "GlobalStorage.h"
@@ -186,7 +188,20 @@ DebugWindow::DebugWindow()
         }
     } );
 
+    // Tools page
     connect( m_ui->crashButton, &QPushButton::clicked, this, [] { ::crash(); } );
+    connect( m_ui->reloadStylesheetButton, &QPushButton::clicked,
+             []()
+             {
+                 for ( auto* w : qApp->topLevelWidgets() )
+                 {
+                     // Needs to match what's set in CalamaresWindow
+                     if ( w->objectName() == QStringLiteral( "mainApp" ) )
+                     {
+                         w->setStyleSheet( Calamares::Branding::instance()->stylesheet() );
+                     }
+                 }
+             });
 
     CALAMARES_RETRANSLATE(
         m_ui->retranslateUi( this );

src/libcalamaresui/utils/DebugWindow.ui

@@ -100,6 +100,13 @@
          </property>
         </widget>
        </item>
+       <item>
+        <widget class="QPushButton" name="reloadStylesheetButton">
+         <property name="text">
+          <string>Reload Stylesheet</string>
+         </property>
+        </widget>
+       </item>
        <item>
         <spacer name="verticalSpacer">
          <property name="orientation">