Some small features implemented

Feature list: [list] [*] [b]Level Progress Saving[/b]: Your progress is now saved — you no longer have to restart levels when revisiting. [*] [b]Resizable Sub-windows[/b]: Adjust the size of each section (Code, Output, Goal, Input) to your preference. [*] [b]Clearer Code Block Separators[/b]: Improved visibility of code block dividers and clearer movement restrictions. [*] [b]Reset Progress Option[/b]: Start fresh anytime by deleting all your progress. [/list]