Add rank attribute to DvP

[dmaclean]

Having the rank gives some perspective to the DvP value, since otherwise there's no frame of reference as to what's good or bad.

[dmaclean]

Done. Added rank attribute to DefenseVsPosition. Also created a calculate_dvp_rank script that can be added to all_tasks.sh. This way we’re not relying on the projection generation process to calculate the rank for us, which is a slightly awkward approach.

Files modified:

• basketball.sql
• dfs_constants.py
• models/defense_vs_position.py
• models/defense_vs_position_manager.py
• projections.py
• utilities/init.py
• utilities/calculate_dvp_rank.py
• unittest/all_tests.py
• unittest/test_defense_vs_position.py
• unittest/test_calculate_dvp_rank.py