Add omero_web_python_addons to preinstall additional pip packages

[Simon Li]

ome/ansible-role-omero-server#36 includes the parameter omero_server_python_addons to install pip packages when the venv is created. An analogous parameter could be added to this role to simplify installation of web apps.

• See ome/prod-playbooks#182

You'll need to duplicate the task https://github.com/ome/ansible-role-omero-web/blob/2.0.2/tasks/web-install.yml#L119 since omero.web includes a requirements file (unless you want to decouple omero.web so it's pip installable 😀)

[Josh Moore]

unless you want to decouple omero.web so it's pip installable

I would think that will be achieved by the end of the year.