[Completes #53361411] Third-party applications can uniquely identify a MyUSA user by a MyUSA unique id

 - Partial commit for homogenous UUID generation. Implements authentications, partially.

 - Adds tests for UUID in profile API. Updates method for querying/inserting omniauth authentications.

 - Specifies rb-readline version in Gemfile.

 - Adds index to authentications table for UID column. Updates API and tests to utilize 'id' for UUID field rather than 'uid'.

 - Re-order groups in Gemfile, update warden gem to 1.2.3.

 - Change index on authentications to [:uid, :provider]

 - Slight refactoring.