[completes #57929406, #58977820] Add User model to Deathstar to be able to track logged in user and record refresh token, so that we can request a new token if/when the current one has expired.
This required switching the low-level HerokuAPIV3 over from accepting a token parameter to accepting a user parameter for an ActiveRecord User object.
Also fixed rake spec from the root -- works now.
Remove spec/dummy/config/database.yml which hadn't been ignored due to a malformulation in the .gitignore -- also fixed.