Feat/lists

Merging might be an issue here because I think Ming deleted some of the skeleton .java files that defines our core classes from his branch. It might be better to merge the business logic code with master first. THEN merge Ming's code using "ours" strategy. Like this:

git merge -s ours MingYangPlayTest 

With the ours strategy, git merge will automatically use the local version of the file whenever there is a conflict.