Remove duplication of NoisyWorkflow invocations

We want these two methods to be as similar as possible, so sharing
more code without duplication is a good thing.
Break RootController#index into a set of smaller methods

These methods are far from ideal and mix side-effects (setting instance vars)
with return values in an awkward way. The intent of these changes is to begin
breaking the main method into smaller pieces to make it a little clearer how
it's constructed and how we might move to a cleaner implementation.
Tidy up broken out RootController#index methods

Broken up a little more, and no longer setting instance variables
all over the place. I think this is probably as far as we want to
go without opening up the question of breaking this out into filter
classes and/or revisiting how the AdminRootPresenter works.