Add fantasy points as a metric option for DvP and baseline stats calculations

[dmaclean]

It would be helpful to know what a player's season average is for fantasy points and how many fantasy points an opponent gives up to each position.

Currently, we can fetch average fantasy points from _calculate_scoringstddev, which doesn't make a ton of sense. It was kind of stuffed in there, but adding it to _getbaseline would be a better place.

[dmaclean]

Done. Modified calculate_defense_vs_position to handle a metric of “FANTASY_POINTS”. This required extending the model to have a site parameter, since asking for fantasy points doesn’t really work if we don’t know what site’s scoring system we’re using. Also refactored the call in Projections to use the logic in DefenseVsPositionManager (we actually just lifted the SQL query from Projections).

Files modified:

• basketball.sql
• defense_vs_position.py
• defense_vs_position_manager.py
• projections.py
• test_defense_vs_position.py
• test_dvp.py
• test_projections.py