Update Handling of SSO Linking

[aaronskiba]

Fixes #900
Changes proposed in this PR:

• Update the handling of SSO linking in some user case scenarios.

[lagoan]

This is a good start.

There are a couple of places that could be improved.

[closenma]

Proposed English:
That email appears to be associated with an existing account. \ Sign into your existing account, and you can link with SSO from the 'Edit Profile' page.
Translation is standing by to get us a quick version in French

[closenma]

Got back from translation - small rephrase on both - use these versions, please

English: That email appears to be associated with an existing account. \ Sign into your existing account, and you can link that account with SSO from the 'Edit Profile' page.

French: Il paraît que cette adresse couriel est dejà associée à un compte existant. \ Veuillez vous connecter à votre compte existant, et vous pouvez le lier à l'aide de la fonction SSO à partir de la page 'Modifier le profil'.

[lagoan]

LGTM!

[lagoan]

LGTM!

[aaronskiba]

bundle exec rspec ./spec/integration/openid_connect_sso_spec.rb:42 has an outdated button name. The test passes when I update it. If I change it I lose the PR approval, but I have no one to re-approve. Merging as is.

$ bundle exec rspec ./spec/integration/openid_connect_sso_spec.rb:42
To use retry middleware with Faraday v2.0+, install `faraday-retry` gem
Copying Bootstrap glyphicons to the public directory ...
Copying TinyMCE skins to the public directory ...
Run options: include {:locations=>{"./spec/integration/openid_connect_sso_spec.rb"=>[42]}}

Randomized with seed 11395
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Top 1 slowest examples (1.91 seconds, 55.2% of total time):
  Openid_connection SSO with correct credentials does not create SSO link when user is signed out and SSO email is an existing account email
    1.91 seconds ./spec/integration/openid_connect_sso_spec.rb:42

Finished in 3.47 seconds (files took 4.85 seconds to load)
1 example, 0 failures

Randomized with seed 11395