Features support

Hi,

Cool work.

Some things:
- there is already work on exportability of the CAPTCHA module at #825088: Exportables support for CAPTCHA points
- the exporting seems to work from the superficial testing I did, but how is the importing suposed to work? I tried to override exported values and to revert them through the features UI, but that didn't seem to work

best,
soxofaan

@lesergi Nice work!

@soxofaan After your commits in #825088-28: Exportables support for CAPTCHA points the above patch basically works (including importing/reverting).

But the feature would always appear overridden because of two things:

1. Through captcha_captcha_default_points_alter(), features expects the module-declared defaults to be rendered in hook_captcha_default_points(), and will complain if they're not.
2. The above hook integration is provided by Features, so we need to add it as a dependency.

The attached patch addresses both of these issues, and works well from my testing so far.