Added a Play 2.0.4-esque Json parser for Concept

A few small changes:

* added a Json reader for the Concept model. Note: Play 2.1 has changed this syntax slightly to improve the way errors are caught, see: http://mandubian.com/2012/09/08/unveiling-play-2-dot-1-json-api-part1-jspath-reads-combinators/
* removed target, .target, and logs dirs from SCM