XWIKI-18782: Space and Page related REST resources are failing when a space name contains a slash

* Since we cannot use List<PathSegment> (and neither List<String>) to get the list of URL-decoded space names from Restlet we have to parse the space names ourselves but for this we need the raw, URL-encoded, space path and for this we need to use the @Encoded annotation. This doesn't break the usage of the REST API. It affects only the resource implementations which all use the same API to parse the space path.

(cherry picked from commit 8c62f7be)