added software renderer. split common functions prev.

in gleswidget to renderstack (a QStackWidget), which in
turn calls an actual renderer. added ability to target GLES
directly, but this is maybe uneeded.

src/qt/CMakeLists.txt

@@ -20,8 +20,13 @@ add_library(ui STATIC
     qt_machinestatus.hpp
     qt_mediamenu.cpp
     qt_mediamenu.hpp
-    qt_gleswidget.cpp
-    qt_gleswidget.hpp
+    qt_rendererstack.cpp
+    qt_rendererstack.hpp
+    qt_rendererstack.ui
+    qt_softwarerenderer.cpp
+    qt_softwarerenderer.hpp
+    qt_hardwarerenderer.cpp
+    qt_hardwarerenderer.hpp
 
     qt_settings.cpp
     qt_settings.hpp