Theme system

Solves #1

Can choose between QtCreator's themes and base Vivy theme, or system's theme.

Depends on !21 (merged)

src/VivyApplication.cc

 #include "VivyApplication.hh"
 #include "UI/MainWindow.hh"
 #include "UI/DockWidgetTitleBar.hh"
+#include "UI/Theme/Theme.hh"
 #include "Lib/Document/VivyDocumentStore.hh"
 #include "Lib/Document/VivyDocument.hh"
 #include "Lib/Script/ScriptStore.hh"
@@ -40,6 +41,8 @@ VivyApplication::VivyApplication(int &argc, char **argv)
     }
 }
 
+VivyApplication::~VivyApplication() noexcept {}
+
 void
 VivyApplication::setTheme(Theme theme) noexcept
 {
@@ -48,6 +51,14 @@ VivyApplication::setTheme(Theme theme) noexcept
         return;
     }
 
+    else if (theme == Theme::QtCreator) {
+        qtCreatorThemePtr.reset(new Vivy::Theme("QtCreator"));
+        QSettings settings(QStringLiteral(":theme/design.creatortheme"), QSettings::IniFormat);
+        qtCreatorThemePtr->readSettings(&settings);
+        qtCreatorThemePtr->applyToApplication();
+        return;
+    }
+
     const QString sheet = theme == Theme::Dark ? QStringLiteral(":qdarkstyle/dark/style.qss")
                                                : QStringLiteral(":qdarkstyle/light/style.qss");
 
@@ -82,8 +93,8 @@ VivyApplication::exec() noexcept
     setAttribute(Qt::AA_DontShowIconsInMenus, false);
     setAttribute(Qt::AA_DontShowShortcutsInContextMenus, false);
     setFont(getApplicationFont(Font::Default));
-    setTheme(Theme::Dark); // TODO: Set system theme for now (because we
-                           // don't have a central theme provider).
+    setTheme(Theme::QtCreator); // TODO: Set system theme for now (because we
+                                // don't have a central theme provider).
 
     // Cursor blinking
     setCursorFlashTime(0);
@@ -105,7 +116,7 @@ VivyApplication::exec() noexcept
 
     case ApplicationType::GUI: {
         // Show the main window, also set up the log console
-        mainWindowPtr               = std::make_shared<MainWindow>();
+        mainWindowPtr               = std::make_unique<MainWindow>();
         QDockWidget *logConsoleDock = new QDockWidget("Console", mainWindowPtr.get());
         LogConsole *logConsole      = new LogConsole(mainWindowPtr.get());
         std::shared_ptr<ConsoleLogSinkDispatcher> consoleLogSinkDispatcher =