add relations between trading schemes and regulatory elements

[amanda-wein]

Description of the issue

(comments from Silvia Weko)

For some policies, it would be cool to add that they’re only possible when combined with a regulatory element. This is true in the following cases for trading schemes:

• “green certificate trading scheme” and “white certificate trading scheme” are enabled by “quota”
• “greenhouse gas emissions trading scheme” is enabled by “emissions cap”
• “offsetting scheme” is enabled by “offsetting rule”

Workflow checklist

• I am aware of the workflow in CONTRIBUTING.md

[silviaweko]

I looked at the relations in OWL which I think are just from RO - how about "complies with"? the definition is just "adheres to policies or rules specified in"

[amanda-wein]

That works for me, just made those changes