* mostly light code-style changes and removal of unused code and old TODOs
* removed Escape shortcut for exiting Hightail (Alt+F4 is already in place and is more intuitive)
* changed Ctrl+Shift+C shortcut to Ctrl+C for copying testcases (ProblemJPanel.java)
* fixed bug where exception was thrown when user pressed Ctrl+[Shift+]C while no row was selected in the table (ProblemJPanel.java)