Placing the defense buildings

In this task, we work on the board and allow the player to add buildings.

Prepare for lift off

We are going to need some new files, the helpers and buildings. Specifically, they are helpers.js, building.js, space-junk.js, satellite.js, satellite2.js, castle.js, and castle2.js. Create these files and include them into the HTML file. Also, note that the buildings are placed inside the scripts/board-objects/buildings/ folder:

<script src="scripts/helpers.js"></script>
<script src="scripts/board-objects/buildings/building.js"></script>
<script src="scripts/board-objects/buildings/space-junk.js"></script>
<script src="scripts/board-objects/buildings/satellite.js"></script>
<script src="scripts/board-objects/buildings/satellite2.js"></script>
<script src="scripts/board-objects/buildings/castle.js"></script>
<script src="scripts/board-objects/buildings/castle2.js"></script>

The first helper...