Add json mods field

[Syriiin]

Why?

We require json mods for full lazer support.

Changes

• Add mods_json field to scores
• Rename is_classic to is_stable and determine by legacy_score_id nullness
  • NOTE: Requires manual fix of is_stable=True score=0 scores (lazer scores using the CL mod wrongly marked as stable)
    • and any scores set since Improve lazer score support #171 as score will not be 0 for lazer scores
• Add temporary backfilljsonmods command
• Fix get_bitwise_mods not adding DT when NC is set (and for SD/PF)
  • NOTE: Requires manual fix of existing bitmods where NC/PF are set without DT/SD