Multiple changes

Posts: Added keywords functionality.
Posts: Edit posts inline (Not submitting yet).
Authentication: Make login via user interface possible for editing posts
inline.
Style: Moved global styles (e.g. links, login) to seperate stylesheet.
Login: Changed doctype to HTML5.
Error handling: Option to show error in post themed style.
Meta tags: Added 'description', 'author' and 'keywords' tags.
Menu: Starting support for menu's.