GitLab

* new model Service
* new management commands for handling the services
* remove ASTAKOS_CLOUD_SERVICES setting
* change get_services API call to return
the Service objects
* separate admin from service API calls
* introduce send_feedback service API call

Refs: #2413

Refs: #2019

Refs: #2019

* welcome_email.txt template location
* in activateuser do not change user's state in case of send_email failure
* fix inviteuser

Added the following commands:
* activate user
* create user
* list invitations
* list users
* modify user
* show invitation
* show user

Refs: #1993

Refs: #1997

* move login and setting cookie in one place (prepare_response)
* delete cookie in logout
* delete unused imports
* change requires_anonymous to redirect to logout with next

-incorporate CsrfViewMiddleware
-change tamplates to render forms
-change email template location
-api.activate() returns only information about token
- In prepare_response, instead of setting the cookie, log the user in
- use django.contrib.auth.views for reseting and changing user password

Ref: #1874

- extend django user model
- pass template_name and extra_context in views
- incorporate context processors
- use different backends for invitations and simple workflow

Refs: #1823