add mainpage, add todo entity, add todo dto, add get endpoint

frontend/package-lock.json

frontend/package.json

frontend/src/App.vue

frontend/src/components/LoginPage.vue

frontend/src/components/MainPage.vue

frontend/src/main.js

frontend/src/router/index.js

...va/com/cloudcomputing/todo/controller/UserController.java

src/main/java/com/cloudcomputing/todo/dto/TodoDTO.java

src/main/java/com/cloudcomputing/todo/dto/UserDTO.java

src/main/java/com/cloudcomputing/todo/entity/Todo.java

src/main/java/com/cloudcomputing/todo/entity/User.java

src/main/java/com/cloudcomputing/todo/mapper/TodoMapper.java

...va/com/cloudcomputing/todo/repository/TodoRepository.java

...ain/java/com/cloudcomputing/todo/service/UserService.java