Our (create) linked-objects API call only allows for a subset of compatible CRM objects.

We should match all of the compatible CRM objects that our CRM AddOns are configured for.

For Hubspot, that would be:
* Contact
* Company
* Deal

For PipeDrive, that would be:
* People/Person
* Organization
* Deal

If we can link to the object from the AddOn, then our API should handle it as well. The allowable Salesforce objects seem to follow this model by allowing for multiple objects/tables.