Updates an existing user by email address

<user>
	<name>AHarrison</name>
	<full_name>Ashley Harrison</full_name>
	<email>[email protected]</email>
	<email_address>[email protected]</email_address>
	<phone_number>123-555-6789</phone_number>
	<position>Teacher</position>
	<sites>
		<site>
			<id>-1</id>
			<name>None</name>
		</site>
	</sites>
</user>