Don't resave cells on stopping creation, fixes #74

We was saving everything again when the players stop creating anything,
this was causing issues with duplicate cells when using any storage with
SQL (due to insert and no primary key).

Also, added a hasChanged to the cell class which will prevent resaving
things in sql if it hasn't changed.

src/main/java/com/graywolf336/jail/command/subcommands/JailStopCommand.java

@@ -33,8 +33,6 @@ public class JailStopCommand implements Command {
 
         if(nothing) {
             sender.sendMessage(ChatColor.RED + "You've stopped creating....nothing.");
-        }else {
-        	jm.getPlugin().getJailIO().saveEverything();
         }
 
         return true;