PDF processor now generates HTML

The old image-based PDF processor has been replaced with one
that uses `pdf2htmlEX` and generates an html file for each page.
Cleaned up config.js jsdoc and PDF processor
Fixed-up the jsdoc for timeouts in ./config.js.
Expanded the filters than can be applied when reprocessing content
Merged master in pdf2html
#656 - Allow for updating multiple config elements with ConfigTestsUtil
#656 - Added internationalizable field

This required some refactoring of how data is stored/retrieved in/from
Cassandra. All fields now have a `toDBValue` and `toJSONValue`.

Also added a method to retrieve the latest updated timestamp for a single
config element.
656 - Terms and conditions

2 new config elements are available.
One for enabling the T&C check and one for the actual text

The text is suppressed in the config but can be retrieved from
/api/termsAndConditions

When the T&C is enabled,  create-user requests will need to set the
`acceptedTC` parameter in the create-user request to true.
When a user signs in via an external authentication strategy the T&C
can be accepted by setting the `acceptedTC` parameter to `true` in the
update-user request.

All non-anonymous POSTS requests not going to /api/auth or /api/user
will be checked.
#656 - Return epoch rather than null when a config field hasn't been updated
Add more JSDoc for the new filtered reprocess previews endpoint
Added more test coverage for the regenerate previews filters
Merge branch 'master' into 656-terms-and-cond

* master:
  Documentation changes and re-ordering of slideshare import
  Documentation improvements
  Renamed `done` callback function in importUsers
  add unit test
  add revision back to the content body modified event
  #664 - TincanAPI test failure fixes
  #663 - Fix intermittent failure when importing users.
  fix outdated preview image on activity feed
  #652 - Fix for PP error when SlideShare urls contain querystring params
#656 - T&C code clean up
Special /api/user/:id/termsAndConditions endpoint + bunch of cleanup
Returning acceptedTC timestamp when creating a user + test cleanup
Merged master in 656-terms-and-cond
Merged master into 656-terms-and-cond
Merged master in 656-terms-and-cond
Merged master into pdf2html
#656 - No longer using regex for path checking, using req.ctx.locale to determine request locale.