This commits makes sure that cloudflared starts using the new API
endpoints for managing routes.
Additionally, the delete route operation still allows deleting by CIDR
and VNet but it is being marked as deprecated in favor of specifying the
route ID.
The goal of this change is to make it simpler for the user to delete
routes without specifying Vnet.
cloudflared tail will now fetch the management token from by making
a request to the Cloudflare API using the cert.pem (acquired from
cloudflared login).
Refactored some of the credentials code into it's own package as
to allow for easier use between subcommands outside of
`cloudflared tunnel`.
João Oliveirinha
Devin Carr
Nuno Diegues