Update styles.css

added support for required field (HTML5)
added border:none; for logos and delete deprecated border="0" html attribute
Update html.php

added required attribute to allowed list for input fields
Update login.html

deleted deprecated border="0" Attribute and use css instead
Update header.html

deleted old border="0" attribute and use css instead
Update rcmail_output_html.php

added required Attribute to Login fields
Update mail.html

deleted deprecated frameborder Attribute and use css instead
wrong closing DIV tag
Update addressbook.html

deleted deprecated frameborder attribute and use css instead
Update settings.html

deleted deprecated frameborder attribute and use css instead
Update func.inc

added missing ID for label
Update mail.html

added old frameborder Attribute for IE7 and IE8
Update addressbook.html

added old frameborder Attribute for IE7 and IE8
Update settings.html

added old frameborder Attribute for IE7 and IE8
Merge pull request #96 from Dennis1993/patch-6

Added required attribute and delete deprecated border attributes
Fix downloading binary files with (wrong) text/* content-type (#1489267)