Remove unnecessary use of "safe" template tag.

This tag marks a variable as not requiring escaping by the template engine,
potentially creating cross-site scripting vulnerabilities, so shouldn't be used
unless absolutely necessary. In these cases, I don't think it's necessary.

Rename "supporter" to "sustainer" in templates and URLs.

Does not rename the models.

Sponsors — note in paragraph above that sorting order has changed.

The database entity id is now being seeded by the load script with
the supporter id in front of the entity id, so the sorting will now
be in order of when they joined.

Sponsors: Correct ratio for maximum 250x250 as required.

The image wasn't square like the old one was, so it was stretched with the
previous formulation.

HPE no longer a sponsor of Software Freedom Conservancy.

HPE sponsorship expired and they did not renew.

Remove Linux Foundation from Sponsors page.

Their grace period has ended and they have not renewed their
contribution.

sponsors: Unlist too-old sponsors.

These companies have not given in the past year.

Fix alt tag for Collabora

Thanks to Paul Wise for pointing this out.

Clarify text that not all sponsors are here.

Some sponsors remain anonymous. This text should reflect that.

Wording changes and typo fixes for Supporters.

Update information about who can become a Supporter (small companies
can, too), and make sure they're called "Conservancy Supporters"
throughout.

Place Supporters counter on front & sponsors pages

The number of current supporters now appears on the frontpage and the
sponsors page.

Support anonymous supporter listings by count.

Remove anonymous listing from the alphabetical supporters list and
instead list them by count found.

Supporters list built dynamically.

Hitherto the supporters list has been committed directly to the static
sponsors/index.html file. This was never ideal and a quick hack to
build Conservancy's supporters list at the beginning of the supporters
program.

With this change, a Django app now exists that dynamically generates the
supporters list.

The database rows must be built from Conservancy's internal Ledger file,
which will be done in a separate script.

Rename file to template.

Since we'll produce dynamic content onto this page going forward, this
apparently needs to be in the templates directory now.