GRN2-140: Added Email to inform user they've been promoted (#534)

* Added Email to inform user they've been promoted

* Update user_mailer.rb

* Send email when a user is demoted

* Change more-info string

app/views/user_mailer/user_demoted.text.erb

@@ -0,0 +1,26 @@
+<%
+# BigBlueButton open source conferencing system - http://www.bigbluebutton.org/.
+#
+# Copyright (c) 2018 BigBlueButton Inc. and by respective authors (see below).
+#
+# This program is free software; you can redistribute it and/or modify it under the
+# terms of the GNU Lesser General Public License as published by the Free Software
+# Foundation; either version 3.0 of the License, or (at your option) any later
+# version.
+#
+# BigBlueButton is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+# PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License along
+# with BigBlueButton; if not, see <http://www.gnu.org/licenses/>.
+%>
+
+
+<%= t('mailer.user.demoted.subtitle') %>
+
+<%= t('mailer.user.demoted.info', url: @url) %>
+
+<%= t('mailer.user.demoted.more-info') %>
+
+<%= @root_url %>