fix mode handling and get back to original modes behaviour

 - we have to create AndroidGraphicsMode in case we have mode of
   different type not based on AndroidGraphicsMode (GraphicsMode
   for example), so that we don't get cast exceptions when using
   Mode property

 - do not set EglRenderBuffer in config spec as it is causing
   trouble. it was introduced in context life cycle patch. so
   we get back to original behavior of not setting it. I will
   look at it later, but now we don't want regression

 - this fixes problem where apps setting GraphicsMode changed
   behavior and might end up with much worse mode than before.
   TexturedCubeES30-1.0 sample was good example of that