CYB-359 Only process new Vimeo videos
 * adds a 'submitted_at' field to check against what is being reported by the API

https://jira.ets.berkeley.edu/jira/browse/CYB-359
Merge pull request #221 from coyote/query_vimeo_only_once_per_item

CYB-359 Only process new Vimeo videos