feat: Introduce Device Sidebar Widget and Settings Management

- Removed TabWidget
- Added DeviceSidebarWidget and DeviceSidebarItem classes for managing device navigation in a sidebar format.
- Removed the obsolete DeviceTabWidget class and its associated files.
- Updated MainWindow to integrate DeviceManagerWidget for device management.
- Implemented SettingsManager and SettingsWidget for user-configurable settings.
- Enhanced the main application to support settings loading and saving.
- Updated UI to accommodate new settings and device management features.

src/settingsmanager.cpp

@@ -0,0 +1,22 @@
+#include "settingsmanager.h"
+#include <QSettings>
+
+#define DEFAULT_DEVDISKIMGPATH "./devdiskimages"
+
+SettingsManager *SettingsManager::sharedInstance()
+{
+    static SettingsManager instance;
+    return &instance;
+}
+
+SettingsManager::SettingsManager(QObject *parent) : QObject{parent}
+{
+
+    m_settings = new QSettings(this);
+}
+
+QString SettingsManager::devdiskimgpath() const
+{
+    return m_settings->value("devdiskimgpath", DEFAULT_DEVDISKIMGPATH)
+        .toString();
+}