Create device model and setup devise, activeadmin and rspec!

- with attributes: model, imei_number, unique_id and access_token
 - access_token is automatically generated on create

app/admin/dashboard.rb

@@ -0,0 +1,33 @@
+ActiveAdmin.register_page "Dashboard" do
+
+  menu priority: 1, label: proc{ I18n.t("active_admin.dashboard") }
+
+  content title: proc{ I18n.t("active_admin.dashboard") } do
+    div class: "blank_slate_container", id: "dashboard_default_message" do
+      span class: "blank_slate" do
+        span I18n.t("active_admin.dashboard_welcome.welcome")
+        small I18n.t("active_admin.dashboard_welcome.call_to_action")
+      end
+    end
+
+    # Here is an example of a simple dashboard with columns and panels.
+    #
+    # columns do
+    #   column do
+    #     panel "Recent Posts" do
+    #       ul do
+    #         Post.recent(5).map do |post|
+    #           li link_to(post.title, admin_post_path(post))
+    #         end
+    #       end
+    #     end
+    #   end
+
+    #   column do
+    #     panel "Info" do
+    #       para "Welcome to ActiveAdmin."
+    #     end
+    #   end
+    # end
+  end # content
+end