Adapting File Open From Tabris.js Snippets

Added file open example, copied from docs, then modified into a page class, see changeset Add file open example for what we have currently.

Had trouble with just copy pasting PreviewView over as is, so removed temporarily but would like to try to implement it as a standalone class like we did for our page implementation and see if we can get it to go like that, could be a fun little exercise and I'm always a fool for fun 😊