SPARK-1078:  Replace lift-json with json4s-jackson.

The aim of the Json4s project is to provide a common API for
Scala JSON libraries.  It is Apache-licensed, easier for
downstream distributions to package, and mostly API-compatible
with lift-json.  Furthermore, the Jackson-backed implementation
parses faster than lift-json on all but the smallest inputs.

Author: William Benton <willb@redhat.com>

Closes #582 from willb/json4s and squashes the following commits:

7ca62c4 [William Benton] Replace lift-json with json4s-jackson.