Code Cleanup

-Added id to animal objects
-Created setAnimalTotal method
-Created clearExtras method, which is run when switching animal types.
Also visibly unchecks checked extras.
-Improved many comments and removed unnecessary/obvious ones
-Removed a lot of debug related console logging
Added Senior Checkbox

-Added checkbox for the senior discount.
-Added custom checkbox styling.
-Added "isSeniorChecked()" method.
-Added author/project information comment