It is confusing to have the plan type constants not be namespaced
by the thing they represent. We already have a namespacing
convention in place for constants, so we should use it for
Realm.plan_type as well.
This is a prep commit for the Stripe checkout migration.
The Stripe migration commit adds a lot of new view functions. Keeping
all of the views in one view file makes it super hard for readbability.
So creating a new views folder and splitting the existing view file into
two so that we minimize the changes in the big migration commit.