Move omniauth form partial to a component

This way we simplify the view a little bit and replace some slow system
tests with faster component tests.

app/components/devise/omniauth_form_component.html.erb

@@ -0,0 +1,20 @@
+<div class="row">
+  <div class="small-12 column">
+    <div class="margin-bottom">
+      <strong><%= t("omniauth.info.#{action}") %></strong>
+    </div>
+  </div>
+
+  <% oauth_logins.each do |login| %>
+    <div class="small-12 medium-6 large-4 column end">
+      <%= link_to t("omniauth.#{login}.name"), send("user_#{login}_omniauth_authorize_path"),
+                  title: t("omniauth.#{login}.#{action}"),
+                  class: "button-#{login.to_s.delete_suffix("_oauth2")} button expanded",
+                  method: :post %>
+    </div>
+  <% end %>
+
+  <div class="small-12 column auth-divider">
+    <span><%= t("omniauth.or_fill") %></span>
+  </div>
+</div>

app/components/devise/omniauth_form_component.rb

@@ -0,0 +1,22 @@
+class Devise::OmniauthFormComponent < ApplicationComponent
+  attr_reader :action
+
+  def initialize(action)
+    @action = action
+  end
+
+  def render?
+    oauth_logins.any?
+  end
+
+  private
+
+    def oauth_logins
+      [
+        (:twitter if feature?(:twitter_login)),
+        (:facebook if feature?(:facebook_login)),
+        (:google_oauth2 if feature?(:google_login)),
+        (:wordpress_oauth2 if feature?(:wordpress_login))
+      ].compact
+    end
+end