Show more options in relations drop down

Background

The relation drow down (select2) currently contains about 5 items. In some situations this is a low number, for example when many images have the same title.

Requirements

• Increase the number of items to 100. The select2 box should already support this. (if not we need to re-refine this issue)

Technical change

Current JSON URL: /admin/content/?relation=media&limit=5&sort=title&_format=json&q=titl*
New JSON URL: /admin/content/?relation=media&limit=100&sort=title&_format=json&q=titl*