Added the calculator.
TODO: Write the logging feature.

 Initial commit

 Changes to be committed:
	new file:   .gitignore
	new file:   LICENSE
	new file:   README.md
	new file:   build-calculator-Desktop-Debug/calculator
	new file:   build-calculator-Desktop-Release/calculator
	new file:   build-calculator-clang-Debug/calculator
	new file:   calculator/calculator.cpp
	new file:   calculator/calculator.hpp
	new file:   calculator/calculator.pro
	new file:   calculator/calculator_button.hpp
	new file:   calculator/constants_dialog.cpp
	new file:   calculator/constants_dialog.hpp
	new file:   calculator/deployment.pri
	new file:   calculator/expression_edit.cpp
	new file:   calculator/expression_edit.hpp
	new file:   calculator/file_manager.cpp
	new file:   calculator/file_manager.hpp
	new file:   calculator/history_dialog.cpp
	new file:   calculator/history_dialog.hpp
	new file:   calculator/history_entry.hpp
	new file:   calculator/main.cpp
	new file:   calculator/main.qml
	new file:   calculator/main_window.cpp
	new file:   calculator/main_window.hpp
	new file:   calculator/normal_view.cpp
	new file:   calculator/normal_view.hpp
	new file:   calculator/qml.qrc
	new file:   calculator/scientific_view.cpp
	new file:   calculator/scientific_view.hpp