Added better error messages and made some small adjustments

- Added checks if noitem and limitedcreative should even be used.
- Moved some booleans into the config cache.
Moved the updater class to own package.

I did this because it is not possible to have 2 different classes by the
same name in the same package in java. If you had another plugin using
h31ix' system, TR's updater or that plugin's updater would break.