Adding following API from oae-following sample module
(Following) Following with search, activity and most tests
(Following) Refactored activity routing in a step to make it 'configurable'

* Fixed memberships search indexing for following
* Moved routing to activity-level configuration
* Introduced L1-cached "associations"
* Moved "producer" and "transformer" into single "activity
  entity type" registry
(Following) Fix unit tests and add more for following and activity
(Following) Changes from self-review
Merged master
(Following) Switch to using AuthzConstants.* for visibility and joinable
(Following) Remove validation on start parameter. This isn't done anywhere else
(Following) Adding isFollowing and canFollow to full user profile
(Following) Following up on first set of review
(Following) Adding unit tests for paging of followers and following feeds
(Following) Fixed bad merge where copying tenants was lost
(Following) Followed up on further review feedback
Merge branch 'master' into following

Conflicts:
	node_modules/oae-principals/lib/api.user.js
(Following) Fixing issue with redelivering orphaned single aggregate activities
WIP mediacore
#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