Add versioned outcomes schema

[sei-vsarvepalli]

This is an attempt to move towards Policy Explorer which requires Outcomes and resolves #589 so we have a schema for the outcome groups.

Here is what has happened

1. Outcomes Schema description under data/schema/v1 and data/schema/current (symlink)
2. Outcomes JSON files under data/json/outcomes
3. Create CVSS Vectors that were predefined to create JSON format in data/json/decision_points/cvss/
4. Scripts to create CVSS decision_points and Outcomes in data/json/outcomes

Mostly additions should not disturb any setup.

[ahouseholder]

I'm fine with the bulk of this PR as-is. My only to blockers to merge are:

• do we need data/json/decision_points.zip?
• do we need src/ssvc/gini_impurity.py

both of these seem out of place to me.

[ahouseholder]

Purely a syntactical note, not worth changing, just mentioning it since I noticed it here.

with open("...","w") as f:
    f.write("foo")

does the same thing but you don't have to explicitly close() because the context manager handles it for you.

[sei-vsarvepalli]

will do with syntax...

[ahouseholder]

Also note that we'll need to do a brief reconciliation of #674 with this one, just depends on merge order which one will need to change.