* rename local variables in main file
* additional renaming of functions and variables
* Rename main file functions
* Rename functions and variables in canvas.py
* Rename functions and locals for remaining files
* Rename non-Qt derived class' members
* Rename members of Qt-derived classes
* Fix paint label issue
* Add item single click slot in labelDialog.py
In the original code, double clicking a list item will set the text property and automatically validate afterwards, with the label dialog window disappearing.
In this revised version, double click behavior is unchanged, while single click is added. When single clicking a list item, it will only set text in the QLineEdit. Users can change the text by clicking other items before validating themselves by clicking yes.
