Added a help and about screen

Must remember to finish the about screen

 Changes to be committed:
	modified:   Calculator.pro
	new file:   aboutwindow.cpp
	new file:   aboutwindow.h
	new file:   aboutwindow.ui
	modified:   calculatorwindow.cpp
	modified:   calculatorwindow.h
	modified:   calculatorwindow.ui
	new file:   helpwindow.cpp
	new file:   helpwindow.h
	new file:   helpwindow.ui