Add 'copy' and 'rename' values for the 'method' parameter

The 'copy' and 'rename' operations are very common and are not supported by the REST API. Every client needs to implement them by making 2 or 3 requests for each item instead of 1 and generating unnecessary noise and traffic also impacting performance.

We could extend the 'method' parameter used to overcome browser limitations and add these 2 extra actions to properly do the work.

More details here: http://xwiki.markmail.org/message/56fu6d4piz5a3jrk