Fix so Login screen now works correctly with Umbraco UI Localization settings.

Fixed the issue that meant the Login screen was hard coded to always be in English, now it will respect the "umbracoDefaultUILanguage" setting in the web.config if set, this is now used by default unless a user has just logged out with a different language setting.

http://issues.umbraco.org/issue/U4-4585

Also added a couple more Spanish translations to the Language file.