Individual layers can now be exported separately.
List of layers now fills available space.
Licensing and attribution is now organized somewhat better.
License info can be copied to the clipboard easily now.

Other layout tweaks to the license info window.
Apparently tkinter needs its clipboard cleared each time you want to copy new.
Copy confirmation when "copy to clipboard" is pressed.

Also, disable text entry on the textbox.  Update TODO.
Minor layout polish