feature(extractors/images): Extract all images

Goose used to extract only main image (top_image).
Now it extracts all images from content.

Closes #1
feature(extractors/images): Image test files
fix(extractors/images): Return images from known elements if its size is greater than 0
fix(extractors/images): Add new lines in the end of image test files
Merge pull request #2 from cronycle/feature/1-all-images

feature(extractors/images): Extract all images