This PR makes the following changes:

* Defaults to the edx.org zone instead of a vpc zone
* Takes an AWS id and secret to query another account for instance info
* Adds some safe guards around duplicate dns entries
* Creates an ban list for elbs

- Adds new utility class for DNS entries
- Delays adding records to the end as one batch
- Alters the noop flag to output XML
- Fails if the run would require a delete
- Adds a force flag to make delete explicit

* pep8 updates
* adding more comments
* refactoring
* adding examples