Don't require schemes for FROM and APPLY

[pcoccoli]

Is your feature request related to a problem? Please describe.
The hunter doesn't care if an analytic is using docker or python.

Describe the solution you'd like
APPLY my_analytic should work whether it's a python- or docker-based analytic. Similarly FROM my_datasource should work without having to specify stixshifter://my_datasource.

Maybe we have something in config that lists interface preference order? E.g. python,docker so it checks python first, then docker. Stop at first match.

You could still supply the scheme, to force the one you want in case of name collisions.

Describe alternatives you've considered
Leave it like it is now.

Additional context
N/A