Prepare for Supporters beyond 750.

After the next import, we'll have more than 750 supporters. This change
not only handles that fact, but adds sufficient Javascript and Django
templating to handle the case if the Supporter count for any reason
drops below 750 again.

Create renewal option on form.

This adds a renewal option to the form.

site-wide supporter count fundraiser.

Using the jQuery UI multiprogress bar added earlier, this change allows
display of the of the progress bar on every page.