added PlayerMarks to save combinations of player names and associated marks (refs #16 @10m)
fixed wrong saving of Vote when voting users up or down

Signed-off-by: Markus Andree <me@hapm.de>
added stats command to the StatsCommandsExecutor (closes #16 @3h)

Signed-off-by: Markus Andree <me@hapm.de>