[WIP] Upickle -> Json4s

[manuzhang]

Be sure to do all of the following to help us incorporate your contribution
quickly and easily:

• Make sure the commit message is formatted like:
  [GEARPUMP-<Jira issue #>] Meaningful description of pull request
• Make sure tests pass via sbt clean test.
• Make sure old documentation affected by the pull request has been updated and new documentation added for new functionality.

[codecov-io]

Codecov Report

Merging #245 into master will increase coverage by 0.5%.
The diff coverage is 87.71%.

@@            Coverage Diff            @@
##           master     #245     +/-   ##
=========================================
+ Coverage   69.07%   69.57%   +0.5%     
=========================================
  Files         192      192             
  Lines        6166     6186     +20     
  Branches      540      521     -19     
=========================================
+ Hits         4259     4304     +45     
+ Misses       1907     1882     -25

[manuzhang]

Blocked on json4s/json4s#397