Send email and im notifications

[abelozerov]

When:

1. Merge request is created, for merge masters
2. Merge is accepted or rejected, for requester and all collaborators (QA, code review guys) taken part in merge request

[lehabaev]

Please use send_html_mail(subject,message, message, settings.EMAIL_HOST_USER, [user])
This app add email to db and cron send mail.