Bug Fixes/Checker Tweaks

Fixed Issue #1 from DoubleDoorDevelopment/Pay2Spawn
Fixed Issue #2 from DoubleDoorDevelopment/Pay2Spawn

All checkers now default to disabled
Changed default polling interval to 20 seconds to avoid being locked out
of remote systems
Move minimum donation amount to a per checker setting
Moved Donation Tracker URL to configuration setting
Added MD5 hash functionality to Helper class
Donation tracker checker now uses MD5 hash for unique ID until the API
actually supplies a unique value
Added isPlayerOpped method to Helper Class for later use