Schematics context now have an (optional) analytics field that, if set,
should be used to report usage. This can be set even in some cases where
analytics is disabled (to a noop analytics).
And receives in its constructor the enginehost and registry. This simplifies the creation
of the NodeWorkflow, or later on the Google3Workflow etc, since all the duplicate logic
is now in a single base class.
This is yak shaving for internal stuff.
