#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
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  fix outdated preview image on activity feed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
#656 - No longer using regex for path checking, using req.ctx.locale to determine request locale.
Merged master
#656 - Cleaned up ConfigAPI.
Removed .toDBValue and converted skinning to new config structure.
Added needsToAcceptTC on create.
#656 - PR cleanup

 * All status codes >= 400 are considered errors in the unit tests
 * Return 419 if T&C hasn't been accepted yet
 * Re-arranged locale checking for T&C
 * clearConfig can clear optional keys
 * ConfigTestUtil.clearConfigAndWait takes array rather than single string
 * Added more test coverage
Fixes for less 1.5.0 upgrade

less 1.5.0 includes the full License header, so the tests now reflect this
Clearing multiple optional elements should work.
Fixed up lint issue.