Configured to use spring-framework.
Added MainPageController to show a welcome page instead of removed index.jsp.
And also added MainPageControllerTest to test MainPageController.
'servlet-api 3.0' was added as dependency module for testing to avoid error in spring-test.
Merge pull request #4 from yusukemasuda/feature/#3

Checked this pull request that the application will show a welcome page generated with spring-webmvc, and close #3