Previously, the railties required by the project gemspec was in conflict with
the rails versions being pulled in by Appraisal.
There were situations where a newer rails app was generated by `rails new...`
even though the Appraisal gemfiles/ value should have been setting it correctly.
We need to be able to use the versions of things specified in the appraisal gemfiles/
specify the version of rails for the initial generation of the applications,
but subsequently allow those applications to point to the `Gemfile` within
the newly generated rails apps, rather than wherever BUNDLE_GEMFILE was previously
set by Appraisal.
The factory name for the model Namespaced::User wil be :namespaced_user.
The :class option is specified as a string to prevent class reloading issues.
Addresses GH-44
