Authorization intializer fails with a pre-Devise db

[orenyk]

Steps to reproduce:

1. Seed DB in version v3.4.x
2. Checkout code post v5.2.0
3. Try to run rake db:migrate (i.e., update)

Expected: success
Actual: NoMethodError: undefined method username' for #User:0x007f1b0309e1e0`

I'll get this done now, I'll just skip the initializer unless User.respond_to?(:username).

[orenyk]

Note that this actually affects databases prior to v4.1.0, not v3.4.x exclusively. Also, note that migrating a v3.4.10 DB actually results in a slightly different schema (object created_at and updated_at timestamps have null: false), but I'm not checking it in since the current db/schema.rb results from a fresh checkout + rake db:migrate.

[orenyk]

Just realized, the schema issues could stem from a bad schema in earlier versions. Regardless, nothing to be done.

[orenyk]

Also, ready for review!