Speed up the DvP calculations for regression

[dmaclean]

DvP calculations run way too slow and are currently why regression takes 15 minutes to run. Speed that shit up.

[dmaclean]

Fixed. Added a _defense_vsposition table so we can quickly generate a cache for the _Projections.calculate_defense_vsposition() function.

Files modified:

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