CAS + SAML authentication feature (#6425)

* Cas authentication feature

* Config

* Remove class_eval + Omniauth initializer

* Codeclimate review

* Codeclimate review 2

* Codeclimate review 3

* Remove uid/email reconciliation

* SAML authentication

* Clean up code

* Improve login form

* Fix code style issues

* Add locales

db/migrate/20180204034416_create_identities.rb

@@ -0,0 +1,11 @@
+class CreateIdentities < ActiveRecord::Migration[5.0]
+  def change
+    create_table :identities do |t|
+      t.references :user, foreign_key: { on_delete: :cascade }
+      t.string :provider, null: false, default: ''
+      t.string :uid, null: false, default: ''
+
+      t.timestamps
+    end
+  end
+end