[Feature request] Demo mode!

[RowanDDR]

To make it super easy for new users to see and hear SNES Tracker "singing and dancing", let's include a demo.sts file with SNES Tracker. Something simple and pleasing that has some standard elements such as a lead, beat, bass, and a few patterns.

• On first run of SNES Tracker the user could be prompted "Would you like to open a demo song?". On second thought, that's somewhat patronizing and annoying/intrusive. 😬
• Perhaps better, the demo could be easily loaded from the file menu... after Recent Files let's have a pre-populated Demo Files list?
• The demo could be your Say So song (or a slimmed down edit).. or my crappy attached demo (which needs cleaning up.. too many empty instrument fields).
  https://mega.nz/file/ZPQQWLAK#AOAAvOcEfL_ugISHSFRaCRRMQvR6WVXDIb5AKdEtZFc