Merge feature SOL-20

This is a pull request to merge the SOL-20 feature (https://openedx.atlassian.net/browse/SOL-20).
@martynjames  - We're certainly abstracting the relevant column values here with our file category grouping, but the thought it that this small list will help authors achieve the goal of finding an asset whose type they may know (Image) but not necessarily format (png. jpeg, jpg, etc.)