Prev/Next and Count/Total-Count headers for ListResults

[mschulkind]

Any DSU request that returns a list of data support the num_to_skip and num_to_return parameters. They also return a number of headers describing the omitted data and links to the next/prev pages.

There are currently a number of issues with this.

1. These values are broken in a number of places including the SchemaIdsRequest and any shim request.
2. The MultiValueResult and MultiValueResultAggregator and related code that are supposed to handle deriving these values is brittle, awkward, and hard to understand, leading to breakages such as in item 1.
3. The shim interface does not support passing back the information required to correctly calculate these values, and even if it did, it's not always possible for a shim to calculate the required data.

My recommendation is to just remove all of this and let the user page through the data and stop when they encounter then end (empty request).