CYB-226 Engagement Index should be frequently, automatically, updated

* introduces sidekiq, clockwork, and clockworkd to do the work
* each of the two types (discussion and submissions) has its own async call
* adding a few scripts to help with the setup and maintenance
Merge pull request #161 from coyote/clockwork

CYB-226 Engagement Index should be frequently, automatically, updated
CYB-273, deploy.sh script should fail when 'git fetch origin' returns non-zero
Merge pull request #162 from johncrossman/CYB-273

CYB-273, deploy.sh script fail when 'git fetch origin' returns non-zero
CYB-274 - Comment submit button throws 'id' not defined error, not submitted

https://jira.ets.berkeley.edu/jira/browse/CYB-274
Merge pull request #163 from christianv/CYB-274

CYB-274 - Comment submit button throws 'id' not defined error, not submitted
CYB-275 - Insecure content warning in the console when loading images from Vimeo

https://jira.ets.berkeley.edu/jira/browse/CYB-275
Merge pull request #164 from christianv/CYB-275

CYB-275 - Insecure content warning in the console when loading images from Vimeo
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CYB-278 - Remove outdated public dummy json files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CYB-278 - Remove outdated public dummy json files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