Improve REST API

 add new ApiController

the new controller will answer to the `/api/...` urls
using these you can configure even more generic REST interfaces at the expense of losing a container identity.
if you set up `X-Container-Meta-Rest-Endpoint` on the container to a `swift://` url and use the `/api/...` path info
the application or job description will be loaded from that url and executed instead of usual container operation
the original storage-related operations will still be available under `/v1/...` url