Github: add spacer rows around Application setup
Github: rewording application help text strings

Make it clearer what the Github Application Client ID and Secret are
used for.
Fix PHP notice
Use specific error message for empty required field
Fix HTML/CSS for account update form
Replace deprecated <acronym> element by <abbr>

Reference: http://www.w3.org/TR/html5/obsolete.html#acronym
Remove calls to helper_alternate_class()
HTML/CSS fixes for manage_config_page.php

Use a form-container div instead of table
HTML/CSS fixes for SourceSVN config

Use divs instead of table rows/cells
HTML/CSS fixes for index.php