Upgrade traverse_thredds to manage newer versions of THREDDS catalogs

[steingod]

The current version of the thredds_client Python package doesn't work with newer TDS catalog implementations. Find a workaround for this.

[steingod]

thredds_client has been forked and modified, now it seems to work at least for some datasets, further testing is needed.

[steingod]

Some modifications in package nc_to_mmd as well. Will clean up code and submit for furtehr testing. thredds_client modifications are more comprehensive and need further cleaning and testing.

[steingod]

Some minor modifications of traverse_thredds have been made but not committed yet. Preparing a PR for thredds_client now.

[steingod]

PR (bird-house/threddsclient#15) on thredds_client that fixes issues on TDS v5 has been submitted, still some work to do on HYRX implementations.