Update screenshots and files that reference them

The screenshots are more recent (including some new ones).

The welcome email images have not been updated as some things have to be
answered before that can be done.

The current files were renamed to be shorter as well.

next/register.html

@@ -456,10 +456,10 @@ in order to register for the IOCCC.</p>
 <blockquote>
 <p>Subscription consent for ‘ioccc28-reg’</p>
 </blockquote>
-<p><strong>NOTE</strong>: Beware that your email service, application and/or Internet
-Service Provider (ISP) might modify email subject lines. For example, some string
-might have been prepended or appended to the subject line. Beware of
-this when you search for the Subscription consent” email.</p>
+<p><strong>NOTE</strong>: be aware that some email services, applications and/or Internet
+Service Providers (ISP) modify email subject lines. For example, some string
+might have been prepended or appended to the subject line. Be aware of
+this when you search for the “Subscription consent” email.</p>
 <p><strong>NOTE</strong>: The “Subscription consent” email is usually sent by the FreeLists
 List Manager within a minute after clicking the <strong>((Next &gt;&gt;))</strong> button.
 If you don’t see the “Subscription consent” email, check your spam folder.</p>