Admin: Decide what to do with "Change password" page

[angela-tran]

When logged in as a native Django user account, you'll see a "Change password" link in the usertools section.

That link takes us to a page that we have not overridden / that doesn't use our extrastyles, so it uses all the default Django styles.

Originally posted by @angela-tran in #2371 (comment)

We should decide if we're keeping this page in and if we should style it like the rest of the agency-facing pages.

[angela-tran]

I wanted to see what this page would look like if I made some bare minimum changes, like

• import our admin styles and Bootstrap into the page
• remove sections like the breadcrumbs and sidebar so it matches our other pages

This is the result:

Before	After

I'll open a draft PR that shows the few code changes that were needed to get this.

There's a template that's shown after the user successfully changes their password (registration/password_change_done.html), so I'd need to do the same thing for it:

[angela-tran]

Here's what password_change_done.html looks like with the same type of minimal code changes:

(Caveat: I did add the "Back to dashboard" button)