Refactor drush config-packager-generate-packages into drush features-export

Problem/Motivation

The config_packager has a "generate-packages" drush command for exporting config into modules. This becomes the new features-export command.

Proposed resolution

In Features D7 there was "update" and "revert". This was confusing to people and originated from the Views UI terminology. In config_packager we have the "generate" terminology. In Features D8 we want to use "export" and "import" to better match the core CMI terminology. "Generating" a module is the "export" process.

We also want the list of packages to export to be space-separate similar to the "drush en" and other core drush commands, rather than using csv as in config_packager.