[ACHYDRA-1029] Update omniauth-cul to 0.3.0

[goldsmithb]

Jira Ticket

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This PR upgrades our omniauth-cul gem version to 0.3.0, which comes with some breaking changes and includes a developer strategy of its own.

This PR:

• replaces the custom code we had to use the devise developer strategy with the omniauth-cul provided developer_uid strategy (less finagling of devise routes on our part -- much simpler setup)
• replaces the :cas strategy with the :columbia_cas strategy (new implementation from omniauth-cul)
• adds a flash success message after signing in
• removes omniauth-rails_csrf_protection gem (not needed in omniauth v2+)

[JackBlackLight]

This looks great @goldsmithb