Create the elastic search query in a more precise and flexible way

[alexgarel]

What

• Right now we extract bare words from the query in unknown operation and filter them out to treat them separately.
• But the implementation is quite faulty:
  • at least we should harvest words as we remove them from expressions
  • we should verify in the transformer if we are in a SearchTerm or not !

Proposed solution

• But if we want to support complex expressions, instead of separating bare words, we should specialize the elastic search query builder so that it handles our bare words using our target expression.
• Also we should support Phrase, not only Word.

Part of

• 🎯 What can I work on ? (search-a-licious) #62

[alexgarel]

I changed the implementation to be more straightforward while keeping the full text term / filters separation.

It's good enough for now but this ticket will be kept open because the good solution is to correctly change the Word search as we transform the tree to an ES query.