Switch CCS upload, copyright assignment, FOSSY and podcast components to use path()

This is the newer approach to URL routing in Django.

Add the conservancy-www-db.path Systemd file

This runs the SQL update when the relevant file is modified.

Add linkchecker Systemd service and timer

Doesn't yet email report of errors.

Remove nesting of hidden sections on sustainer page

This makes the page more similar to how it has worked in previous years.

fossy: check UUID format in the URL routing to avoid unhandled exception

Requests like /fossy/xyz123/ were causing an error due to "xyz123" not being a
valid UUID. We should just return a 404 in this case, which the URL routing will
now do automatically.

Fix "expand all sections" second link

Issue was that the jQuery is using .children() to add the event handlers but due
to some changes to the HTML, the second link is no longer a direct child. I've
switched this to .find() instead.

Provide a default for DEBUG

This avoid having to specify it in the production environment config at all -
shorter config.

Remove CONSERVANCY_SECRET_KEY

Use SECRET_KEY instead to minimise use of non-standard settings.

Add to-do file

This allows me to track improvements we'd like to make, but not necessarily
straight away.

Simplify settings and move some standard settings into settings.py

These were previously in djangocommonsettings.py, but don't ever vary between
development and production environments.

Update .gitignore to reflect directory structure changes

Also removed some unused ignore lines.

Eliminate "conservancy" and "apps" subdirectories

The directory nesting is unnecessary here and confusing to navigate. I've moved
all apps to the project subdirectory, currently called "www", but soon to be
renamed "conservancy".

I've also moved manage.py to the top-level directory.

Add Use the Source mockup pages

This doesn't include any data models yet.

Allow "outercontent" template block to use full page width

This allows us to create full-width layouts for specific campaigns.

Remove unused modpythoncustom.py

We have used mod-wsgi for many years.

Fix podjango migrations

Required an updated following code restructuring.

Switch to relative imports

The relative imports make it clearer what code is within the project and where
it's coming from.

podjango: Factor out credits, feedback and license info

This makes it easier to keep up-to-date across multiple templates.

podjango: Link up "The Corresponding Source" title

This helps with navigating back to the home page.

Merge podjango.apps.cast into main podjango module

It's much simpler if "podjango" is the name of the Django app with a single
urls.py etc. The reason this is required is because podjango was originally a
fully-blown Django website and now it's become a Django app within the
Conservancy website.

Remove www/conservancy/static/admin

These files are copies from an old version of Django, causing display issues in
the newer Django admin. With the "staticfiles" app enabled, the recent versions
of these files are copied to /var/www/website/collected-static/ when you run the
"collectstatic" management command. For example:

sudo -u www-data /var/www/venv-website/bin/python manage.py collectstatic --link

assignment: Prevent unhandled error when fields not provided

This typically happens when a bot is submitting the form. This should be a
validation error rather than an unhandled exception.

Rename cast to "The Corresponding Source", move to URL prefix "/cast/"

Also improved detail view rendering where unclosed <ul> tags in the body
content HTML from the database were affecting the display of footer info.

Don't serve tachyons from staticfiles just yet

We need to consolidate the static files all at once.