Fetch and use command argument datatypes from server

To increase the flexibility of the client, the datatypes for each argument in each command should be retrieved from the server, rather than held locally. This commit adds this capability, while still using the `navigate.yaml` file on the client if the server does not provide information. The `navigate.yaml` file will be considered deprecated, since the server will provide this information moving forward.

Note: This required a re-recording of the VCR specs, since it issues a second GET for detailed command information.
Note: This changes the format of the `navigate.yaml` file slightly, in order to be compatible with what is expected from the server.

Fixes https://tickets.puppetlabs.com/browse/RAZOR-216