Add support for DMS video delivery (#146)

* Add support for DMS video delivery

Continues work on #139

* Reorder generic method

* Capture progress and failures, use tqdm, overwrite without prompt

* Add -r warning

* Fix warning

* Check for overwrite, support --break-on-existing

* Accept the clumsy paramters check, for now

* Use .part for downloads that were interrupted

* Reconsider -r support

* Use return

* Always overwrite .part files, clarify behavior when they exist