Add solution for recipe_0046 and a helper to keep things neat.

[markpbaggett]

What Does This Do

This adds a solution for recipe 0046 and a helper called add_rendering(). I added the helper so that one did not need to pass values as a list (i.e. rendering=[rendering]). The helper is attached to all classes in skeleton that has an optional rendering property and each of those classes are included in tests.

[glenrobson]

Could this be done by using the auto list helper:

https://github.com/markpbaggett/iiif-prezi3/blob/e6810804a9f28ad643934bbdc2ea87d51b805ff2/iiif_prezi3/helpers/auto_fields.py#L153

If I remember correctly this will turn an item to a list if its not passed as a list

[markpbaggett]

Could this be done by using the auto list helper:

https://github.com/markpbaggett/iiif-prezi3/blob/e6810804a9f28ad643934bbdc2ea87d51b805ff2/iiif_prezi3/helpers/auto_fields.py#L153

If I remember correctly this will turn an item to a list if its not passed as a list

@glenrobson, you are right. This is something I forgot (or maybe never knew). I rebased the change to the existing file and git rm the two unnecessary files that were introduced.