[feature/new-tz-handling] Preselect a timezone in registration.

Use Javascript to obtain client's timezone offset and select the
first timezone in our list with that offset.

Changes for prosilver only. The javascript file should be shared
between styles.

PHPBB3-9558

phpBB/language/en/ucp.php

@@ -399,6 +399,7 @@ $lang = array_merge($lang, array(
 	'SIGNATURE_EXPLAIN'			=> 'This is a block of text that can be added to posts you make. There is a %d character limit.',
 	'SIGNATURE_PREVIEW'			=> 'Your signature will appear like this in posts',
 	'SIGNATURE_TOO_LONG'		=> 'Your signature is too long.',
+	'SELECT_TIMEZONE'			=> 'Select timezone',
 	'SORT'						=> 'Sort',
 	'SORT_COMMENT'				=> 'File comment',
 	'SORT_DOWNLOADS'			=> 'Downloads',