Fix for import unit tests; program object export functionality

Follow-up to [PRs 586](https://github.com/reciprocity/ggrc-core/pull/586) and [PR 569](https://github.com/reciprocity/ggrc-core/pull/586):

- Adds export functionality for controls and systems to programs (previously only set up imports).
- Fixes unit tests that were breaking because of the new keys used in the `options` dict.
- Matches directive metadata header to what current template download button gives the user.
- Improved unhelpful key name: the id of an imported object's parent object id is now `parent_id` instead of `object_id`.