Fix to explicitly install cnx-epub with collation support
Fix to explicitly install cnx-epub with collation support

This explicit install like is required, because pip is unable to install
dependencies with requirements extras. The results of this are an application
that complains about missing dependencies.

```pytb
Traceback (most recent call last):
  File "/usr/local/bin/pserve", line 11, in <module>
    sys.exit(main())
  File "/usr/local/lib/python2.7/site-packages/pyramid/scripts/pserve.py", line 32, in main
    return command.run()
  File "/usr/local/lib/python2.7/site-packages/pyramid/scripts/pserve.py", line 253, in run
    app = loader.get_wsgi_app(app_name, config_vars)
  File "/usr/local/lib/python2.7/site-packages/plaster_pastedeploy/__init__.py", line 131, in get_wsgi_app
    global_conf=defaults)
  ...
  File "/usr/local/lib/python2.7/site-packages/paste/deploy/loadwsgi.py", line 645, in find_egg_entry_point
    pkg_resources.require(self.spec)
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 895, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/local/lib/python2.7/site-packages/pkg_resources/__init__.py", line 781, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'cnx-easybake; extra == "collation"' distribution was not found and is required by cnx-epub
```

Connexions/cnx-publishing,Connexions/cnx-publishing,Connexions/cnx-publishing