add java interface

Ok. 
1) the "incomplete" means that there exists a PS interface and two demo applications, nor all applications. 
2) We have made no modification to the C++ code when we are writing the interface. Our interface is just related with the API of petuum. If the API is changed, we need to amend some interface descriptions on our interface files. 
3) Can you open the coming version of Petuum for us to see the modification about API?