Add images to fragments and testimonia

[raquelalegre]

Always mentioned as low priority. We'll need need more reqs: e.g do we need field for pic author, caption, hyperlink?

If it's only just one picture per fragment/testimonia/original text would be easy to do.

[acholyn]

technically the base has been laid with #453 since CK Editor has this ability (used in commentaries and introductions). If image uploading is desired that will need to be set up but it works with links at present

[acholyn]

not essential at present but if going to implement, enable uploading and image captions