Broker service needs to make correct links for data access.

The broker service works ok against Hyrax servers because the dataset URL is the same as the download URL. However in TDS servers:

1. file access is granted using a different server.
2. DAP2 access uses a different service
3. Is there even a DAP4 service available in the TDS?

Regardless the catalog service stack needs to be evaluated. Broker links should be built using a prioritized list of available services. It seems like getting the file is maybe the first choice, modulo the fact that the TDS support formats that Hyrax does not ( .gini, .grib, etc). Evaluating what is a serviceable format is more than the OLFS/XSLT is going to do so if we can get a DAP4 data response then we should because we know that it will have all of the dataset content, and that we can read it.
Broker Retrieval Priorities:

1. DAP4
2. DAP2 (If we get .dods and .das can we then build a DMR?)
3. File

Thoughts?