CYB-270 Support for filter by assignments in the Gallery, include assignment name

  * new Assignment model (so requires migration)
  * hooks into the assignments_processor to get assignment data
  * only adds one SQL query/type (image/video) per clock tick, plus one
      SQL write per assignment
  * action /index on assignments added

  NEW ROUTE:
  /api/v1/assignments
Merge pull request #165 from coyote/assignments_api

CYB-270 Support for filter by assignments in the Gallery
CYB-277 - Front-end: Add filter by assignment / Fix filter by types

https://jira.ets.berkeley.edu/jira/browse/CYB-277
CYB-278 - Remove outdated public dummy json files

https://jira.ets.berkeley.edu/jira/browse/CYB-278
CYB-279 - conent_type should be content_type

https://jira.ets.berkeley.edu/jira/browse/CYB-279
CYB-276 - Submit button for editing a gallery item comment is failing

https://jira.ets.berkeley.edu/jira/browse/CYB-276
Merge pull request #169 from christianv/CYB-276

CYB-276 - Submit button for editing a gallery item comment is failing
Merge pull request #168 from christianv/CYB-279

CYB-279 - conent_type should be content_type
Merge pull request #167 from christianv/CYB-278

CYB-278 - Remove outdated public dummy json files
Merge pull request #166 from christianv/CYB-277

CYB-277 - Front-end: Add filter by assignment / Fix filter by types
CYB-271 Support for number of views of Gallery items

Support for tracking views
  * new model, controller, route for views
  * gallery controller will return 'views' count(actually implemented in lib/array_refinement and
     in the attachment and media_url models)