Added New Sites and Selected class

The following changes happened:
1. The subsites for Unternehmen, Dienstleistungen, Produkte and Kontakt
have been added
2. For the user to determine which site he is watching ATM, a (75% in
height) white background is now raised on the selected menu item.
3. Therefore a selected class on the html li element had to be created.

Like it? ;D