Compatibility with new Oauth2 api authentication

  * Removed the last vestiges of the old REST Api.
  * Add Authorization: Bearer access_token header
  * Move some file, comment, etc operations to new api.
upload_version does not take a new_name, and takes the file to upload as the `name` parameter
Remove testing access token.

Developers are required to generate their own access token, which is now
outside the scope of this library.
Correctly catch unsuccessful responses.

@glongman noticed this was incorrectly handling responses, since 'response' is
always a HTTParty::Response and not a Net::HTTPResponse
Use correct namespace for Box::Api::Exceptions

Exceptions were mistakenly referenced as Box::Net and not Box::Api.
Fetch entire contents of a folder before running `find`

This solves the problem raised in Issue #28.