Test exposing bearer token issue
Add some missing dependencies to gemspec.

Also a missed require of omniauth.
Refactor bearer token to use warden-oauth2
Update bearer token fetch to include client_id

This fixes the token transfer issue (see
https://github.com/alphagov/signonotron2/pull/245 for more details)
Update omniauth-gds dependency.

This makes the omniauth user details fetch include the client_id in the
request.
Update gem dependencies to resolve failures.

bundler was failing to achieve a solution to the dependency graph, which
was causing the tests to fail.  Pinning rails at 3.2 as a development
dependency helps this (additionally, the test suite currently assumes a
Rails 3.2 client app, and fails if it's run with rails4).
Merge pull request #51 from alphagov/fix_bearer_token

Fix bearer token transfer issue.