EventLogging refactor

Using "funnel" classes based on the Android code to encapsulate
multi-stage logging funnels/pipelines. The funnels can be passed
from one view controller to the next so things like edit and login
that run over multiple steps can keep their session IDs.

Dropped the 'logEvent:' extension category from UIViewController.
Split the schema list and versions to the various funnel classes.

Confirmed that items make it through to the outside, yay.

Note seem to be missing the ReadingActionFunnel -- fixme!
This has changed upstream or something, so leaving for later.

Change-Id: Ie7e447f4da948b6486515e36a87528ea34393ad0