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
WIP mediacore
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
refactor mediacore into its own module and add rest endpoint
Add more JSDoc for the new filtered reprocess previews endpoint
publish media and sign embed url
Added more test coverage for the regenerate previews filters
fix log name
allow express to accept POSTs up to the limit we set in nginx
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  fix outdated preview image on activity feed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
remove unused video thumbnail sizes
external previews