Handle search misspellings

I modified it because I wanted to avoid the caller to know of Search::Similarity. As Search::Similarity is in the Search scope, I wanted only Search to use it. 

Therefore, it's the Search object that contains the similar term, while the API caller only knows of the starting term. For the API caller to know the similar term, it has to access Search#query. 

The previous version of the API was directly returning the results, as an ActiveRecord::Association, making it impossible to access the Search instance itself, and therefore the query. 

PS: summarising it made me realise that this thing is horrible :worried: