UTF-8, ready to use and finished installation

1. All tables and field names were updated. As a consequence. the
finished installation script create a database which can be used now.
2. The character set was updated. Every string is now UTF-8. But there
is a bug, that the user subjects don't show up umlauts.
3. There is a beginning of an login script
4. There is some code for supporting multiple grading systems (doesn't
finished yet)
5. Some bugs and other small things were eliminated