refactor and clean code

src/main/java/org/hbp/mip/MIPApplication.java

src/main/java/org/hbp/mip/controllers/ApiException.java

src/main/java/org/hbp/mip/controllers/ApiOriginFilter.java

...main/java/org/hbp/mip/controllers/ApiResponseMessage.java

src/main/java/org/hbp/mip/controllers/ArticlesApi.java

src/main/java/org/hbp/mip/controllers/DatasetsApi.java

src/main/java/org/hbp/mip/controllers/GroupsApi.java

src/main/java/org/hbp/mip/controllers/HibernateUtil.java

src/main/java/org/hbp/mip/controllers/ModelsApi.java

src/main/java/org/hbp/mip/controllers/NotFoundException.java

src/main/java/org/hbp/mip/controllers/VariablesApi.java

src/main/java/org/hbp/mip/mock/ArticleMock.java

src/main/java/org/hbp/mip/mock/ModelMock.java

src/main/java/org/hbp/mip/mock/UserMock.java