supporter: Support donors upgrading to supporters.

With a valid URL, a past donor can upgrade to a supporter by donating
the rest of the amount. Django validates the data and, if it passes,
puts it in the form. The JavaScript does most of the work from there.

supporter: HTML5 improvements to form.

* Use "number" type for a better prompt.
* Use new standard "min" attribute for richer validation.

js: Fix math again.

I misunderstood how multiprogressbar works. Values aren't expected to
progressively grow larger; it takes care of the summing itself.

js: Use three-part progressbar when no middle goal defined.

Since our current fundraiser doesn't have a "middle goal," this makes
it a little easier to maintain the template and do the math.

Supporter page: Try #2 for scroll to type selection after window ready.

* Trigger on the "load" event rather than "ready".
* Install the handler outside document's "ready" handler so it should
take effect more reliably.

Supporter page: Make supporter type selections act like tabs.

* Scroll to the type selection when the visitor follows a link to a
specific type.
* Don't scroll the page when the user changes their selection.

Supporter page: Refactor JavaScript.

This isn't intended to have any functional change, it's just DRYing up
the code to simplify functional changes later.

Change bar to show totals in a different way.

The achieved! text is removed, to just show the total Supporters, and
the middle part is how many more we need right now.

Reduce ! in various site-wide fundraising texts.

Surprisingly, given her predilection for exclamation points:

<karen> yeah... believe it or not, I'd rather not have two exclamation points
in the 750 achieved! [20:30]

<karen> and I would also delete the exclamation point after " enforcement
efforts!" in the text above it [20:31]

So this change is made on her behalf.

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.