Spelling correction in xapian bridge

Xapian bridge now performs spelling correction
on a users query and returns the correctedQuery
(which could be an empty string) as part of the
JSON response to client.

[endlessm/eos-sdk#1982]
![dog](https://camo.githubusercontent.com/aec4c3fc2d674f2a4e90ed9e1413d95f204d7445/687474703a2f2f692e696d6775722e636f6d2f48784839716b612e706e67)