economy sellcommand and lost wallet data on server stop fixed

The /sellcommand in economy had two problems:
1, Crashed with Forge 10.13.2.x (GameData.getItemRegistry().getObject() called with null threw NPE)
2, The item search didn't work, tried to compare item names with ids

Also the wallet data was only saved on player disconnect so if the server was stopped while players were still connected those players lose the wallet data.