Add levels folder with empty gates.py file
* begin process of splitting each level into its own file
Add initialization file to levels folder
* converts folder into proper Python package
Add initialization code to levels folder
* loads all modules/levels in folder
Move Gates level into levels folder
Move mirrors level to level folder
Delete levels.py
* all current and future levels will be in their own files
Add new display method specifically for printing foreword
* move foreword.txt outside of text folder
* text folder is getting moved to levels soon
Move level text folder into levels folder
* remove text subdirectory prefix from format.to_txt
* add text subdirectory prefix to display.print_level_intro