Remove Rails 6 warnings

[dannyphillips]

it seems we need to make a few changes for it to be Rails 6 compliant:

DEPRECATION WARNING: Initialization autoloaded the constant Registrar::SessionManager.
Being able to do this is deprecated. Autoloading during initialization is going
to be an error condition in future versions of Rails.

[mcasper]

@dannyphillips what apps did you get this warning in? I don't see this in Sherpa, which is running Rails 6 and using registrar

[jeremy-marcus]

I am getting it in the procore-hacks app. Any thoughts on how to fix it?