Javascript, Localisation

This patch fixes a few bugs / style issues in the javascript, and a typo in the english i18n files.

rememberme.js was turning autocomplete on with no regard to what was in the roundcubemail config or any other setting/state. It was attempting to change the type of a rendered button, which throws errors in IE. Html was being used rather than element generation via jQuery.

'Security reason,' was changed to plural, 'security reasons,' in en_GB and en_US i18n.