Bug 24369: Add CORS support to the API

Bug 24369: Add CORS support to the API

This patch adds CORS support for API requests. It uses the
AccessControlAllowOrigin syspref. To test:

1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/api/v1/auth.t
=> SUCCESS: Tests pass!
3. Set the AccessControlAllowOrigin to any string (for example, *)
4. Use any API testing tool (Postman?) to place a request on the API
=> SUCCESS: The response headers include Access-Control-Allow-Origin,
    containing what you set on the syspref
5. Sign off :-D

Signed-off-by: Andrew Isherwood <andrew.isherwood@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>