Improve config-file errors from /ma setting.

Catches ConfigError and prints its message rather than letting it bubble
up to the command handler as an uncaught exception. This means that
instead of seeing "An internal error occurred...", command senders now
see the underlying error message, as well as a short message telling
them to fix the error in the config-file and reload.

Closes #599

src/main/java/com/garbagemule/MobArena/commands/setup/SettingCommand.java

@@ -1,5 +1,6 @@
 package com.garbagemule.MobArena.commands.setup;
 
+import com.garbagemule.MobArena.ConfigError;
 import com.garbagemule.MobArena.commands.Command;
 import com.garbagemule.MobArena.commands.CommandInfo;
 import com.garbagemule.MobArena.framework.Arena;
@@ -89,7 +90,13 @@ public class SettingCommand implements Command {
 
         // Save config-file and reload arena
         am.saveConfig();
-        am.reloadArena(args[0]);
+        try {
+            am.reloadArena(args[0]);
+        } catch (ConfigError e) {
+            am.getGlobalMessenger().tell(sender, "Failed to reload arena after changing setting, reason:\n" + ChatColor.RED + e.getMessage());
+            am.getGlobalMessenger().tell(sender, "Fix the error in your config-file, then run " + ChatColor.YELLOW + "/ma reload");
+            return true;
+        }
 
         // Notify the sender
         StringBuilder buffy = new StringBuilder();