As an admin I want to retry failed indexing of a Media item

[dennyabrain]

We need to provide affordances in the UI to let an admin user retry failed index jobs.

Some proposed solutions :

1. on every Media's detail page, its index status should be visible. If it is "failed", a user should see a retry button
2. we create a page at /index/:datasetID where an admin can see all the posts with a thumbnail preview along with their index status. admin should be able to filter posts based on their index status and select multiple items or select all and then retry indexing.

[dennyabrain]

Proposed mocks for option 2 from the previous comment