Move application strings into separate namespace

Them being in the overlay controller required them to be static, which
forces the compiler to give them a memory location at compile time. They
also don't really fit into the overlaycontroller.

src/tabcontrollers/AudioTabController.cpp

@@ -64,7 +64,7 @@ void AudioTabController::initStage2( OverlayController* var_parent,
     this->widget = var_widget;
 
     std::string notifKey
-        = std::string( OverlayController::applicationKey ) + ".pptnotification";
+        = std::string( application_strings::applicationKey ) + ".pptnotification";
 
     vr::VROverlayError overlayError = vr::VROverlay()->CreateOverlay(
         notifKey.c_str(), notifKey.c_str(), &m_ulNotificationOverlayHandle );

src/tabcontrollers/ChaperoneTabController.cpp

@@ -540,8 +540,7 @@ void ChaperoneTabController::handleChaperoneWarnings( float distance )
         {
             if ( !vr::VROverlay()->IsDashboardVisible() )
             {
-                vr::VROverlay()->ShowDashboard(
-                    OverlayController::applicationKey );
+                vr::VROverlay()->ShowDashboard( application_strings::applicationKey );
             }
             m_chaperoneShowDashboardActive = true;
         }

src/tabcontrollers/SettingsTabController.cpp

@@ -8,7 +8,7 @@ namespace advsettings
 void SettingsTabController::initStage1()
 {
     m_autoStartEnabled = vr::VRApplications()->GetApplicationAutoLaunch(
-        OverlayController::applicationKey );
+        application_strings::applicationKey );
     auto settings = OverlayController::appSettings();
     settings->beginGroup( "applicationSettings" );
     auto value = settings->value( "forceRevivePage", m_forceRevivePage );
@@ -33,7 +33,7 @@ void SettingsTabController::eventLoopTick()
         if ( parent->isDashboardVisible() )
         {
             setAutoStartEnabled( vr::VRApplications()->GetApplicationAutoLaunch(
-                OverlayController::applicationKey ) );
+                application_strings::applicationKey ) );
         }
         settingsUpdateCounter = 0;
     }
@@ -54,7 +54,7 @@ void SettingsTabController::setAutoStartEnabled( bool value, bool notify )
     {
         m_autoStartEnabled = value;
         auto apperror = vr::VRApplications()->SetApplicationAutoLaunch(
-            OverlayController::applicationKey, m_autoStartEnabled );
+            application_strings::applicationKey, m_autoStartEnabled );
         if ( apperror != vr::VRApplicationError_None )
         {
             LOG( ERROR ) << "Could not set auto start: "

src/tabcontrollers/UtilitiesTabController.cpp

@@ -259,8 +259,8 @@ QString getBatteryIconPath( int batteryState )
 vr::VROverlayHandle_t createBatteryOverlay( vr::TrackedDeviceIndex_t index )
 {
     vr::VROverlayHandle_t handle = vr::k_ulOverlayHandleInvalid;
-    std::string batteryKey = std::string( OverlayController::applicationKey )
-                             + ".battery." + std::to_string( index );
+    std::string batteryKey = std::string( application_strings::applicationKey ) + ".battery."
+                             + std::to_string( index );
     vr::VROverlayError overlayError = vr::VROverlay()->CreateOverlay(
         batteryKey.c_str(), batteryKey.c_str(), &handle );
     if ( overlayError == vr::VROverlayError_None )