Add search suggestions.

[s3rius]

Add REST API for search suggestions.
Best implementation will be:

1. Frontend sends you a request with search query.
2. Backend returns possible suggestions with suggested item type.
   As example:
   Sent by frontend:

{
  "query": "pe"
}

Backend response:

[
  {
    "suggest": "pepperoni",
    "type": "Order item"
  },
  {
    "suggest": "Peaks Island",
    "type": "Seller"
  }
]

[Kolaer]

Added simple search API at /search_api/search.

Parameters:

• query: string. String to query to.
• limit: integer. Limit to number of items. Works independently for each search type (Sellers, Merch.).

Result: json in this format:

• res: string. If it's "ok", then query results are in data, otherwise res is description of error.
• data: array of maps. Array of query's results.
  Each element contains:
  • suggest: string. Contains value to suggest.
  • type: string. Type of suggested item (Seller, Merch.).