Changes to the chunk unloading and the world scrubber.

- Using for each loops where possible as they might be more efficient
but in any case improve readability of the code.
- Moved the check if redpower is enabled out of the for loop so it
doesn't check again for every loaded chunk, but only once. If it is
disabled, it just turns UseRPTimer off so it will not trigger any more.
- Changed some variable names to make them more readable.
- Moved the ticktimer variable out of the for loop so it will only be
calculated once.