#795: New style for messages and menu

To begin, this commit changes the style of the messages (error, message,
tick and cross).
- Use of gradient, box-shadow
- Better look if there is more then 1 line in a message box
- No icons (20 kB smaller! :D)

Other changes are:
- The menu is now 3px removed from the header to keep it on the same
hight as the content
- The menu items now use 2 lines of pixels more (top and bottom)
I know that most of the users won't use the dashboard on a touch device,
but it is possible, this makes it easier
- Fix for reset-buttons, which where blue in browser that doesn't
support CSS3 gradients
- Less border-radius, to keep the design a little bit one big thing
- Sidebar is now displayed on screens whit a small width

As always, preview on http://studio384.be/db/. If you don't like it, I've another concept on http://studio384.be/db2/ :)