Rename "d3m index" to "d3m primitive" CLI

That was the first CLI comand and it was named poorly in comparison with other/later CLI commands. We should bring it in sync with others which operate around the entity they deal with.

We can leave index in place as hidden alias with deprecation message if you use it.

That is important if we will be bring more sub-commands to it (testing of primitives, for example, it makes no sense to call that d3m index test, but d3m primitive test sounds great).