Consider deselecting certain streams by default

[edgarrmondragon]

404 warning - Some endpoints are only available to privileged users, and the API appears to handle this at our site by return 404 if the endpoint is not reachable. I don't know how to handle this error properly in the Meltano SDK - the fix for me would be to "not select" the stream, e.g. I have had varying success querying {accountId}/repositories/ with different API keys.

From #162.

Perhaps selected_by_default can be used for this.

cc @mjsqu