mailman3::web::install changes, fixed spec tests

mailman3::web::install changes, fixed spec tests

This reverts commit 104f4fa4bc7988b4da58ea9b757b944d82884d12.
The custom code needed to add CAS support has been packaged
and now can be installed via pip. It is an appropriate thing to
put in our profile::mailman3 manifest, not here.

Removed web_manage_proxy_config boolean, this is outside the
scope of the module, should be done in a profile elseswhere.

Removed hacky hard-coding of custom Django projectfiles and
added a parameter to pass a puppet file source for the Django
project files. We will provide some by default if the user does not
provide a string.

Deleted "manage_web_server" parameter; it conflicts with default settings
for the python module we are using as a dependency (both want to install
pip). We will configure this in a profile (which is what we are doing
already) and will provide some suggestions to the user in the
documentation.

Fixed rspec tests so that the epel module actually works in the tests
instead of not calling it.

Change-Id: Iaf6c9eca2009c370133391b32ba880e5b183987b
Signed-off-by: Josh Farwell <jfarwell@linuxfoundation.org>