Update config.yml

Added information to configurables.
   Note: i cant think of any reason why a server would want to allow the ability for players to destroy paintings, item frames or vehicles on an island that isn't theirs. Maybe that doesn't need to be in the config and set to deny in the code always?
   Note2:Not added comments for extra-menus section as i'm unfamiliar with what it all means.
Changed sendToSpawn to true by default. Its unlikely servers wouldn't have a /spawn command and this prevents players falling into the void on login. Servers that don't have a /spawn command (a lot less than those that do) can change to false if they need to.
Removed allowPvP: deny as it was a duplicate from the world guard flags section.