references to partial responses

[crotwell]

Here is a first cut at allowing stationXML to refer to responses instead of embedding them directly in a channel.

The basic idea is that PartialResponse is a new element that contains Stages. The PartialResponse is at the same level as Network (so top level element) and Network is now optional.

A Response can now be either a sequence of Stage or a of PartialResponseRef, which has an xlink, fromStageNum and toStageNum to allow it to point to a PartialResponse either in the same file or elsewhere. PartialResponse must have an id for this to work. PartialResponse can also include an equipment resourceId to allow the xml to say that this part of the response corresponds to that piece of equipment associated with the channel.

I have also included some examples:

example-remote-response-ref.staxml - an channel whose response is external, pointing to logger and sensor below
example-logger-response.staxml - just the logger part of a response, such as a nominal response for a particular config
example-sensor-response.staxml - just the sensor part o a response, perhaps nominal
example-internal-response-ref.staxml - an example where the sensor and logger partial responses are included in the xml