Fix position data in player tables

[adror1]

Right now, the position columns for both the player table and the fieldplayer_overall_season_stats table use only the fbref information from the first season a player plays. This is not correct, so two things need to be changed:

1. Ensure the player table's position column uses the position information from all years
2. Allow each year for a player to have different positional data in the fieldplayer_overall_season_stats table.