User delete flag

## User Delete Flag

* Added API method `setDeleteFlag` that will respond to `POST` or `PUT` HTTP methods (`POST` being used for setting the flag, `PUT` being used for resetting it to an empty string).
* Added 5 test cases to the test suite to handle majority of scenarios - need to add more for complete coverage of `setDeleteFlag` 

Open for revisions before it is ready for a merge - to be honest, it probably needs them...

@kentquirk 
Issue reference: #12 
Now that I've taken another look at the function, that does seem to be correct. Do you think it should only be accessible if a server token is present? Would a user performing account maintenance via blip have a server token to use on a delete? Or should it accept a server token or user token?

Sorry for the last minute questions and potential changes.