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/tasks/taiga-back.yml

@@ -0,0 +1,73 @@
+- name: ensure system dependencies are installed
+  package:
+    name:
+    - gzip
+    - libjpeg
+    - python3-psycopg2
+    - '{{ taiga_python_package }}'
+    - sudo
+    - tar
+    - zlib
+    state: present
+  tags:
+  - install
+
+- name: ensure taiga user exists
+  user:
+    name: taiga
+    system: yes
+    home: /var/lib/taiga
+    state: present
+
+- name: ensure taiga dependencies are installed
+  environment:
+    PIP_NO_INDEX: t
+    PIP_FIND_LINKS: '{{ taiga_pip_url }}'
+    PIP_TRUSTED_HOST: '{{ taiga_pip_url|urlsplit("hostname") }}'
+  pip:
+    requirements: '{{ taiga_pip_url }}/requirements.txt'
+    virtualenv: /usr/local/lib/taiga/venv
+    virtualenv_command: '{{ taiga_python_exe }} -m venv'
+    state: present
+- name: ensure taiga-back is installed
+  unarchive:
+    src: '{{ taiga_back_url }}'
+    dest: /usr/local/lib/taiga/
+    remote_src: true
+  notify:
+  - migrate taiga data
+  - compile taiga messages
+  - collect taiga static data
+
+- name: ensure taiga media directory exists
+  file:
+    path: /usr/local/lib/taiga/taiga-back/media
+    owner: taiga
+    group: taiga
+    mode: '0755'
+    state: directory
+
+- name: ensure taiga-back is configured
+  template:
+    src: settings.py.j2
+    dest: /usr/local/lib/taiga/taiga-back/settings/local.py
+
+- name: ensure taiga-back entry point script is installed
+  copy:
+    src: taiga-back.sh
+    dest: /usr/local/libexec/taiga-back.sh
+    mode: '0755'
+  notify:
+  - restart taiga
+- name: ensure taiga systemd unit is installed
+  copy:
+    src: taiga.service
+    dest: /etc/systemd/system/taiga.service
+    mode: '0644'
+  notify:
+  - reload systemd
+  - restart taiga
+- name: ensure taiga starts at boot
+  service:
+    name: taiga
+    enabled: yes