Add sql migration and optimize plugin for big servers

[Rubenicos]

I found multiple problems using the plugin, so I added some changes to fix them.

SQL migration

Instead of offline player migration, this concept obtain data directly from a SQL database. Some plugins like MySQLPlayerDataBridge did not allow me to migrate the data because it did not exist for some players when using Vault API.

Big servers data handling

For example, one of my server modes have more than 350.000 accounts, so I extended the name loading timeout and also created an optimized backup command. Previously, using /backup-economy the plugin took 45 minutes to save accounts into file, now it took no more than 5 seconds.