Fixes #386 - Updated rake puppet:import_classes to support the new API

The rake task now queries for the changes and then performs the update.

Some additional sanity checking is performed in the execution phase.

A batch mode is provided via rake puppet:import:puppet_classes[true]. When
"true" is passed to this task then no user imput is required.

If the file config/ignored_classes_and_environments.yml is present then
its contents are stripped from the set of changes that the puppetclass
import will attempt to do. There is also a self documenting sample file in
extras/ignored_classes_and_environments.yml.sample