Added Manage Groups Shell

...u/drexel/TrainDemo/controllers/users/GroupController.java

src/main/java/edu/drexel/TrainDemo/models/users/Group.java

...ava/edu/drexel/TrainDemo/services/users/GroupService.java

...edu/drexel/TrainDemo/services/users/GroupServiceImpl.java

src/main/resources/static/js/admin.js

src/main/resources/static/js/user.js

src/main/resources/templates/admin/groups.html

src/main/resources/templates/admin/users.html