CS-4956 & SITE-560 & IM-1355: Fixes issue with rich text captions

Fixes:
- When rich text captions are enabled and value is set to 0, text fields
  were uneditable.
- Duplicate image metadata view, when editing metadata via the
  article edit screen, when only one image was attached to the
  article.
- The javascript error when rich text captions are enabled related
  to the previous mentioned bug.
- When uploading a new image via the article edit screen, the 'next'
  button would trigger a javascript error and the page would break.
Merge pull request #650 from m038/IM-1355

CS-4956 & SITE-560 & IM-1355: Fixes issue with rich text captions