CYB-220 - Videos should show the date posted - back-end

Timestamps as returned by the API should be in a JS friendly format, not as strings.

* Front end code from Christian
* Changing Attachment table's 'date' column to a Datetime, rather than a String
* Requires a (destructive) migration
* other than the type change, backend as submitted by Christian

Author:    Christian Vuerings <vueringschristian@gmail.com>
modified by Coyote (craig.a.cook@gmail.com)