fixes issue #4956
previous code only worked for the first 10 domains on the account (as Linode
API returned a paginated response, with only 10 records).
This change makes an exact search query for each subdomain, completely removing any
need for walking through paginated responses. What makes it work for large
accounts with any number of domains.
The Cloud and Classic Manager work with different APIs, and so require
a separate module, which we introduce here.
The README has also been modified to state that the two are separate
and incompatible, and provides instructions on using either.
