frontend-ng#505: enhance the rpc response for Get()

[lukemarsden]

and friends by:

• splitting out explicit server state e.g. active/pushPeerState from human readable description in status
• remove version as it's always zero now?
• spell human readable 'commits' as if we put this text in the UI we want it to make sense

this change is in support of https://github.com/dotmesh-io/frontend-ng/issues/505#issuecomment-500196559