Go gadget for Rails4

Fixes include changes to ```oauth2_provider``` engine and ```OauthRepository.java```. Required updating ```oauth2_provider``` engine to [v1.0.3](https://github.com/sachinsudheendra/gocd_oauth2_provider_engine/releases).

Also @arvindsv updated joda-time version to 2.3 in 91e8e1e
> jruby-1.7.11 includes joda-time 2.3 (see dependencies section
here: http://maven-repository.com/artifact/org.jruby/jruby-core/1.7.11). Go
was using joda-time 1.6. There is an incompatibility in constructors between
these versions, and some oauth code in token.rb#before_create failed, since
it picked up the older joda-time class.