cleaned up claim class
put back claims.getPermissions method

it was still needed for the dynmap-griefprevention plugin
asynchronous file conversion

the legacy file conversion is now run asynchronously, to prevent server
with many players or groups from timing out on startup.

Also overhauled the commandHandler class for better readability. All
commands now have their own method, which is chosen with a case
statement from the GPCommand enum.