Accessibility: Bump heading in members/single/profile/change-avatar.php

[mercime]

Basic rationale: see #6871

Current headings:
<h1>Name</h1>
<h2>username</h2>
change-avatar.php
<h4>Change Profile Photo</h4> => <h2> ... </h2>

[mercime]

Attached patch bumps the heading in the Member Profile > Change Profile Photo screen plus basic style.

Attached before & after screenshots of the screen in the following themes:

• Twenty Ten
• Twenty Sixteen
• Twenty Fifteen
• Twenty Fourteen
• Twenty Thirteen
• Twenty Twelve