Fix rpgnext command showing wrong players

They query included all players on the same level instead of only those
with more experience.
Fix german chat stats phrases being trunced

The topmenu's buffer is too small to display the whole phrase in the
settings menu.
Added antidote upgrade

Allows to reduce duration of bad effects on players.
All effects in the effect hub are supported. Currently burning, freezing
and slow down.
Update README to include optional modules