ActivityExtHandler is a extension handler used by context that wants
to integrate with Activity Streaming. For example, there are two
extension handlers that implement this interface: Connection's Extension
Handler and Group Space's Extension Handler.
Process QueryOptions and return an Evaluated QueryOptions. An evaluated
QueryOptions expands on the options specified in the original query options.
For example, the original query options will just indicate that the
query should return all group space activities of the current user.
The GroupSpace Extension Handler will have knowledge about the
current user's list of group space will need to fill in that information
in the returned evaluated query options.