Retrieve documents from CALMHub in the CLI

[willosborne]

Feature Request

Description of Problem:

Currently the CLI can only work with the local filesystem, and doesn't talk to CALMHub.
There should be a mode where it's configured to point at a CALMHub instance and patterns, schemas, etc are retrieved with the REST API.

Note that this is only about pulling data - we should also consider how the CLI will be used to upload patterns, architectures, etc into CALMHub but this will come later.

Potential Solutions:

Refactor the SchemaDirectory to have two implementations - a file system implementation that is the same as what we have today, and one that uses CALMHub.

Add an option to pass the CALMHub URL. Also potentially add the option to configure this in an init/rc file in the user's home directory. For example, ~/.calm.json

[willosborne]

Currently I have a working spike of this for the generate command.
Some changes to the CALMHub REST API will need to be made, we are discussing these today on the Office Hours.