Fix app losing focus on monitor fullscreen, re-add app fullscreen action to view menu

src/kdenliveui.rc

 <!DOCTYPE kpartgui SYSTEM "kpartgui.dtd">
-<kpartgui name="kdenlive" version="174" translationDomain="kdenlive">
+<kpartgui name="kdenlive" version="176" translationDomain="kdenlive">
   <MenuBar>
     <Menu name="file" >
       <Action name="dvd_wizard" />
@@ -219,6 +219,8 @@
       <Action name="insert_timeline" />
     </Menu>
     <Menu name="view" noMerge="1" ><text>View</text>
+    <Action name="fullscreen" />
+    <Separator />
       <Menu name="layout_save_as" ><text>Save Layout As</text>
 	<Action name="save_layout1" />
 	<Action name="save_layout2" />

src/monitor/monitor.cpp

@@ -829,7 +829,7 @@ void Monitor::slotSwitchFullScreen(bool minimizeOnly)
             m_glWidget->setParent(nullptr);
         }
         m_glWidget->showFullScreen();
-        qApp->activeWindow()->setFocus();
+        m_videoWidget->setFocus();
     } else {
         m_glWidget->showNormal();
         auto *lay = (QVBoxLayout *)layout();