Version checks were not validating that the cli version matched the
control plane or data plane versions.
Add checks via the `linkerd check` command to validate the cli is
running the same version as the control and data plane.
Also add types around `channel-version` string parsing and matching. A
consequence being that during development `version.Version` changes from
`undefined` to `dev-undefined`.
Fixes#2076
Depends on linkerd/website#101
Signed-off-by: Andrew Seigner <siggy@buoyant.io>
Andrew Seigner