Allow async conversion and use a UUID service where possible

src/main/java/com/drtshock/playervaults/converters/Converter.java

@@ -1,5 +1,8 @@
 package com.drtshock.playervaults.converters;
 
+import com.turt2live.uuid.ServiceProvider;
+import org.bukkit.command.CommandSender;
+
 /**
  * Represents a simple converter for converting another plugin's content
  * to PlayerVaults.
@@ -11,10 +14,13 @@ public interface Converter {
     /**
      * Converts the other plugin's data.
      *
+     * @param initiator    the initiator of the conversion. May be null
+     * @param uuidProvider the UUID provider to use, cannot be null
+     *
      * @return the number of vaults converted. Returns 0 on none converted
      * or -1 if no vaults were converted.
      */
-    public int doConvert();
+    public int run(CommandSender initiator, ServiceProvider uuidProvider);
 
     /**
      * Determines if this converter is applicable for converting to PlayerVaults.