Add VTK, GL debug info

Add the following info:

```
VTK Major Version,
VTK Minor Version,
GL Driver Version,
GL Renderer Version,
GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS,
GL_MAX_CUBE_MAP_TEXTURE_SIZE,
GL_MAX_DRAW_BUFFERS, GL_MAX_FRAGMENT_UNIFORM_COMPONENTS,
GL_MAX_TEXTURE_IMAGE_UNITS,
GL_MAX_TEXTURE_SIZE,
GL_MAX_VARYING_FLOATS,
GL_MAX_VERTEX_ATTRIBS,
GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS,
GL_MAX_VERTEX_UNIFORM_COMPONENTS,
GL_MAX_VIEWPORT_DIMS, GL_STEREO,
```

This info should be computed only once and stored as it will use the expensive `glGet` calls. A toolbar info window should then display this stored information.

This will also be useful to the applications that use Mayavi for debugging OpenGL related issues.