Added shortcuts

• Added:
- shortcuts functionality
- shortcuts route, controller, model
- shortcut error message for "exists"
- shortcut redux
- EditShortcutsModal, constant
- links to sidebar, sidebar_xs
- options to add/remove group, account in GroupOptionsPopover, ProfileOptionsPopover
- shortcuts page, feature/list

app/serializers/rest/shortcut_serializer.rb

@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class REST::ShortcutSerializer < ActiveModel::Serializer
+  attributes :id, :account_id, :created_at, :shortcut_type, :shortcut_id
+
+  def id
+    object.id.to_s
+  end
+
+end