Improve Zupfnoter Demo Mode

[bwl21]

Request

• As of now Zupfnoter shows the demo tune only if

  • it is invoked the very first time or
  • user enters "demo" in console

  when Demo tune is loaded the content of localstore is desctroyed. User looses his tune if it was not saved before

• There should be more Demos to be invoked from the Help menu

• It should be possible to create a link which directly opens a tune in Zupfnoter similar to opalrb.org/try

Solution approach

1. Provide URL-Parameters to load demos
   /?load=...&mode=demo
2. if demos are loaded, make them readonly, at least do not store them in localstore
3. provide a share button which crates a link with a compressed url