Make a feathers-ssr behavior that switches between sockets/XHR

~~XHR requests made by the SSR server get stored in the XHR_CACHE. The socket.io client isn't aware of it, so it makes the same requests again instead of using the cached ones.~~

Based on the meeting notes in the next comment, we need to make a behavior specifically for SSR that...

1. Uses XHR requests on the server. The existing CanZone plugin for handling XHRs will populate the XHR_CACHE.
2. Uses XHR requests on the client before re-attachment of the client app to the SSR-rendered DOM. These XHR requests will check the XHR_CACHE.
3. Allows the client to fall through to using another behavior (in our case the `feathers` behavior) on the client AFTER re-attachment.