Exception fix and handling + better usability

Fixed the "No enum constant com.achimala.leaguelib.models.LeagueRankedTier.null" exception at runtime, applied workaround for exception handling fixing specific LeagueErrors as "Summoner not in Game" and "Game not spectateable".
Moved League account and "Summoner to lookup" from hardcoded string to commandline arguments for better usability and debugging.