Add more error handling

Transactional create_hiscores. Do not create lonely Hiscore row if creating of Experience, Rank or Level row fails (for example too high number for Integer to handle).

In the update process retry 3 times with 15 second intervals both fetching the players and getting hiscores for every player if it for some reason fails. At the moment without catching the error the whole update process just crashes and stops if an error occurs for one of the players.