Fix backwards compatibility in google-api-client

#543 broke backwards compatibility. (see here for the ripple effect).

#543 broke apart google-api-client into two packages, but removed some public classes. That type of change requires a major semver change.

In the short term, we need to add a dependency in google-http-client to google-http-client-apache to preserve backwards compatibility until we have a major new release of google-http-client.