add spreadsheet example from Odersky Venners & Spoon book to test sources

[SethTisue]

@Sciss writes at https://github.com/scala/scala-swing/issues/76#issuecomment-385634543 :

Regarding the book examples, the best would probably be to simply drop them into test sources, so we would automatically detect if there is a deviation introduced. I have printed copy of edition 2 somewhere buried, and the PDF of edition 1; could you perhaps - if you have PDF of the latest edition - just send me the code examples, then I can add them. In the version I'm seeing, that's listings 32.1 through 32.4, 33.1 through 33.9 ; or if they've never changed, I can copy them from my sources.

@bvenners do you have the code for this...?

[Sciss]

Ok, sources are here: https://booksites.artima.com/programming_in_scala_3ed/examples/

I'll add them at some point if there is no objection from the publishers/authors. Says license is Apache, so I assume I can simply copy these.

[Sciss]

Fourth edition: https://booksites.artima.com/programming_in_scala_4ed/examples/

@bvenners should we add this code? Seems Apache licensed.