Large database overhaul, several minor changes

Changed database structure, you have to convert now an existing XAseco2
database to UASECO!

Added the possibility to have more then one UASECO
in only one database (prefix for tablenames).

Renamed $aseco->mysqli to
$aseco->db (maybe it is possible to add support for PostgreSQL in
future).

Aligned the struture of Player- and Map-Zone.

Added new
Plugin: Tachometer. =)

Serveral minor bugfixes and changes.