Killstreak tracking is now a configurable option
Block non-OITG commands run by players in arenas
Add permission node to override blocking of non-OITG commands
Refactor listener package in anticipation of custom listener system
[API] Add KillstreakListener interface (see detailed description)

Single-class implementations of the KillstreakListener (stored in a
designated directory in the plugin data folder) enable the creation of
custom killstreak perks.
[API] Add VictoryListener interface to enable the rewarding of arena winners
[API] Add ListenerManager, used to handle custom listeners
[API] Fire events for custom listeners
Don't fireKillstreakChangeEvent when a player with no killstreak dies
[API] Load them listeners!