Project Exercise enhancement: make exercises independent of implementation

[mollyxu]

Currently, there are many project exercises that could be implemented in different languages. For instance, the minesweeper exercise could be implemented in Java in addition to Python. Thus, instead of specifying the implementation every time we create a project exercise, I suggest making the exercise independent of the implementation (this means we should include multiple implementations options with the corresponding resources for each option)

The user should be able to toggle between which language they choose to do the exercise in. In the example of minesweeper, the user should be able to select to do it in Java and see the corresponding resources for making minesweeper in Java.