Split project-specific base tests from note model tests (js)
Add a couple simple tests for models
Refine Topic model in backbone

The id attribute is now a combination of the topic_node_id and the
project slug. This composite attribute is created in the `parse` method
of the Topic model. This means that when feeding data to a Topic,
`{ parse: true }` must be passed in options.
Fix typo in test
Add a RelatedTopicsMixin which updates models' related_topics attr