Connected the signals of the constants dialog with the corresponding slots.
Enhanced the math parser.

 On branch master
 Changes to be committed:
	modified:   build-calculator-Desktop-Release/calculator
	modified:   calculator/calculator.cpp
	modified:   calculator/calculator.hpp
	modified:   calculator/constants_dialog.cpp
	modified:   calculator/constants_dialog.hpp
	modified:   calculator/main_window.cpp