roles/taiga: Deploy Taiga project management app

The *taiga* role installs the three components of Taiga:

* taiga-back
* taiga-events
* taiga-front

*taiga-back* is a Python application. Its dependencies are installed via
`pip` in the *taiga* user's site-packages, and the application itself is
installed by unpacking the archive. *taiga-events* is a Node.js
application. Its dependencies are installed by `npm`, and is itself
installed by unpacking the archive. Finally, *taiga-front* is a
single-page browser application that is installed by unpacking the
archive, and served by Apache.

Taiga requires PostgreSQL and RabbitMQ.

roles/taiga/templates/settings.py.j2

@@ -0,0 +1,26 @@
+from .common import *
+
+MEDIA_URL = "{{ taiga_media_url }}"
+STATIC_URL = "{{ taiga_static_url }}"
+SITES["front"]["scheme"] = "http"
+SITES["front"]["domain"] = "example.com"
+
+SECRET_KEY = "{{ taiga_back_secret_key }}"
+
+DEBUG = False
+PUBLIC_REGISTER_ENABLED = True
+
+DEFAULT_FROM_EMAIL = "no-reply@example.com"
+SERVER_EMAIL = DEFAULT_FROM_EMAIL
+
+#CELERY_ENABLED = True
+
+EVENTS_PUSH_BACKEND = "taiga.events.backends.rabbitmq.EventsPushBackend"
+EVENTS_PUSH_BACKEND_OPTIONS = {"url": "amqp://taiga:{{ taiga_events_password }}@localhost:5672/taiga"}
+
+EMAIL_BACKEND = "django.core.mail.backends.smtp.EmailBackend"
+EMAIL_USE_TLS = False
+EMAIL_HOST = "{{ taiga_email_host }}"
+#EMAIL_HOST_USER = ""
+#EMAIL_HOST_PASSWORD = ""
+#EMAIL_PORT = 25