Come up with the guidelines for use for d3m.primitives namespace

So we can rename primitives if make sure that primitive IDs are fixed and not linked to the name (so for example, a random UUID).

The question is how the use of d3m.primitives namespace should be organized:

• based on author/group names?
• based on interfaces they use (maybe a primitive can even exist at multiple locations)
• based on "primitive family" metadata value?
• some other category?