PR to specify API version in URL

Can people take a look at this PR and test it out.

It gives the option to specify API version in URL as well as in header, like this fqdn/api/v2/hosts

If version specified in both, then current in URL 'wins' over header.

Order of priority

  1. URL - /v1/ or /v2/
  2. header - version=2
  3. default - if neither URL or header is specified.

Let me know if you think otherwise that header should 'win'.

Note, most of the v2 controllers currently fallback to v1 until the open PR #978 is merged which creates separate controllers for all objects rather than fallback to v1