Defining getFirst()

The stub of getFirst() should look like this:

   Item List::getFirst() const {
   }
The steps it should take are:
  1. If I am empty (e.g., mySize is zero):
  2. Return the value of myItem in the Node whose address is in myFirst.
You will need to #include <stdexcept> in order for underflow_error to be declared.