Add like model
Add like_count property to comments
Add API for liking comments
Use english in api urls
Refactor tests
Add tests for model default values
Add likes to comments in templates
Add new API for liking

Changes like API urls to users/<id>/links/likes.
Separates create and delete API endpoints.
Merge pull request #13 from fastmonkeys/feature/liking-a-comment

Feature/liking a comment