Laid down Tree-framework as well as list header

Quick Description of what is needed for LineNumber class:

-Make a LineNumber.cpp file
-Add in the methods specified in the header file in the format I added
in methods in the Word.cpp file

-The addLine function should add the parameter to the end of the list.
-If the number is already in the list, do not add anything to the list

-The getNumber function just returns the value of 'number'

-The print function should print out the current value, and then call
the 'next' variabes print function. If 'next' is null, stop printing