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/files/taiga-back.sh

@@ -0,0 +1,7 @@
+#!/bin/sh
+export PYTHONUNBUFFERED=1
+cd /usr/local/lib/taiga/taiga-back
+exec /usr/local/lib/taiga/venv/bin/gunicorn \
+	--workers 4 \
+	-b [::1]:8001 \
+	taiga.wsgi