Added support for GridImage deprecation in OptsSpec parser

[jlstevens]

This PR addresses issue #1252 by converting 'GridImage' to 'Image' in the opts parser. Here is an example of what it does:

[jlstevens]

@philippjfr In raster.py we have:

GridImage = Image

Would it be worth wrapping GridImage as a subclass of Image, just to issue a deprecation warning in the constructor?

[philippjfr]

Would it be worth wrapping GridImage as a subclass of Image, just to issue a deprecation warning in the constructor?

Not a bad idea.

[jlstevens]

Now when you try to build a GridImage:

[jlstevens]

@philippjfr Ready to review.

I think this PR should make things easier for anyone who might be using GridImage. You could try very fancy things (e.g remapping the option tree) but I think these simple changes should do the trick.

[philippjfr]

This PR addresses issue #1252 by converting 'GridImage' to 'Image' in the opts parser.

This does miss any explicitly assigning to the option tree which I've used in a few places. But since anything else is bound to be complex I'm fine with this since we also have the warning. Will merge when tests pass.