Split alias levels in mentionable and messageable levels. (#5065)

* Split alias levels in mentionable and messageable levels.

* Fixed some tests.

* Set messageable level to everyone by default.

* By defaults, groups are not mentionable or messageable.

* Made staff groups messageable by the system.

app/controllers/groups_controller.rb

@@ -3,6 +3,7 @@ class GroupsController < ApplicationController
   before_filter :ensure_logged_in, only: [
     :set_notifications,
     :mentionable,
+    :messageable,
     :update,
     :messages,
     :histories,
@@ -203,6 +204,16 @@ class GroupsController < ApplicationController
     end
   end
 
+  def messageable
+    group = find_group(:name)
+
+    if group
+      render json: { messageable: Group.messageable(current_user).where(id: group.id).present? }
+    else
+      raise Discourse::InvalidAccess.new
+    end
+  end
+
   def remove_member
     group = Group.find(params[:id])
     group.public_exit ? ensure_logged_in : guardian.ensure_can_edit!(group)