Add messagegroup

Messagegroups are a new kind of group. Every user can join and leave such a
group on her own. They are useful to create topics for mails.

E.g. if there is a weekly newsletter we can create a new messagegroup for
it and every user which is interested in receiving the newsletter can join
the corresponding group.

plugins/messages/app/controllers/admin/messagegroups_controller.rb

@@ -0,0 +1,20 @@
+# encoding: utf-8
+class Admin::MessagegroupsController < Admin::BaseController
+  inherit_resources
+
+  def index
+    @messagegroups = Messagegroup.order('name ASC')
+    # if somebody uses the search field:
+    @messagegroups = @messagegroups.where('name LIKE ?', "%#{params[:query]}%") unless params[:query].blank?
+
+    @messagegroups = @messagegroups.page(params[:page]).per(@per_page)
+  end
+
+  def destroy
+    @messagegroup = Messagegroup.find(params[:id])
+    @messagegroup.destroy
+    redirect_to admin_messagegroups_url, notice: t('admin.messagegroups.destroy.notice')
+  rescue => error
+    redirect_to admin_messagegroups_url, alert: t('admin.messagegroups.destroy.error', error: error.message)
+  end
+end

plugins/messages/app/controllers/messagegroups_controller.rb

@@ -0,0 +1,18 @@
+class MessagegroupsController < ApplicationController
+
+  def index
+    @messagegroups = Messagegroup.order("name")
+  end
+
+  def join
+    @messagegroup = Messagegroup.find(params[:id])
+    @messagegroup.users << current_user
+    redirect_to messagegroups_url, :notice => I18n.t('messagegroups.join.notice')
+  end
+
+  def leave
+    @messagegroup = Messagegroup.find(params[:id])
+    @messagegroup.users.destroy(current_user)
+    redirect_to messagegroups_url, :notice => I18n.t('messagegroups.leave.notice')
+  end
+end