Adding search class for simplesearch

[safwanrahman]

This PR adds a SimpleSearch class for building the Search object of simple search.
So it should work something like this

from kitsune import search as constants
simple_search = SimpleSearch(query="firefox",
                             doc_type=constants.WHERE_WIKI, locale="en-US")
search = simple_search.get_search()
search.execute()

I have tried to follow factory pattern in SimpleSearch, but dont know if totally follow the factory pattern.

This class can be used in simple_search view to build the Search object then paginate and execute. Need to be verified that all the boosting are correct and fields are covered according to previous generate_simple_search function.

Highlight and others are not added yet.

This will made following elasticsearch query. Looking at the json, I think it make sense. Maybe we can compare the old elasticsearch query with this query.

{
  "query": {
    "bool": {
      "should": [
        {
          "bool": {
            "minimum_should_match": 1,
            "filter": [
              {
                "terms": {
                  "document_category": [
                    10,
                    20
                  ]
                }
              },
              {
                "term": {
                  "document_locale": "en-US"
                }
              },
              {
                "term": {
                  "document_is_archived": false
                }
              },
              {
                "term": {
                  "index_name": "sumo_wiki_document"
                }
              }
            ],
            "should": [
              {
                "multi_match": {
                  "fields": [
                    "document_summary^2.0",
                    "document_keywords^8.0",
                    "document_title^6.0",
                    "document_content^1.0"
                  ],
                  "query": "Sample"
                }
              },
              {
                "multi_match": {
                  "fields": [
                    "document_summary^2.0",
                    "document_keywords^8.0",
                    "document_title^10.0",
                    "document_content^8.0"
                  ],
                  "type": "phrase",
                  "query": "Sample"
                }
              }
            ]
          }
        },
        {
          "bool": {
            "minimum_should_match": 1,
            "filter": [
              {
                "term": {
                  "question_is_archived": false
                }
              },
              {
                "term": {
                  "question_has_helpful": true
                }
              },
              {
                "term": {
                  "index_name": "sumo_question"
                }
              },
              {
                "term": {
                  "question_locale": "en-US"
                }
              }
            ],
            "should": [
              {
                "multi_match": {
                  "fields": [
                    "question_title^4.0",
                    "question_content^3.0",
                    "question_answer_content^3.0"
                  ],
                  "query": "Sample"
                }
              },
              {
                "multi_match": {
                  "fields": [
                    "question_title^4.0",
                    "question_content^3.0",
                    "question_answer_content^3.0"
                  ],
                  "type": "phrase",
                  "query": "Sample"
                }
              }
            ]
          }
        }
      ]
    }
  }
}

@pmac r?

[safwanrahman]

Thanks @pmac

[pmac]

re #3294