By mistake, this code would always create a desktop context. The correct
approach is to create an embedded (EGL) context and only fallback to
desktop if that doesn't work.
Starting with OpenGL 4.1 and the ARB_ES2_compatibility extension, desktop contexts can execute OpenGL|ES code. This fallback will allow platforms to execute OpenGL|ES code even if EGL is not available (e.g. Nvidia/Windows).
Removed OpenTK.Graphics.Glu class (reason: deprecated upstream; most functionality provided by OpenTK math; not compatible with OpenGL 3.0+.) OpenTK.Graphics.Glu can be accessed through OpenTK.Compatibility.
Added OpenGL|ES-specific ErrorHelper classes.
Moved OpenTK.Graphics.DisplayDevice and OpenTK.Graphics.DisplayResolution to the root OpenTK namespace (reason: their functionality is not specific and does not depend on OpenTK.Graphics).
Split Graphics*Exception classes into different files.
Made GraphicsErrorException public (reason: necessary for OpenTK.Compatibility).