Returns a query, that is a combination of Q objects. That combination
    aims to search keywords within a model by testing the given search fields.
    search_fields should be something like: [('title', 'iexact'), ('content', 'icontains'), ]

def get_query(query_string, search_fields):
    """
    Returns a query, that is a combination of Q objects. That combination
    aims to search keywords within a model by testing the given search fields.
    search_fields should be something like: [('title', 'iexact'), ('content', 'icontains'), ]
    """
    query = None # Query to search for every search term        
    terms = normalize_query(query_string)
    for term in terms:
        or_query = None # Query to search for a given term in each field
        for field in search_fields:
            q = Q(**{"%s__%s" % (field[0], field[1]): term})
            if or_query is None:
                or_query = q
            else:
                or_query = or_query | q
        if query is None:
            query = or_query
        else:
            query = query & or_query
    return query