Per default: Create a unique-id for filename (so existing files wont get overwrite)

- Adding UUIDv4 per default for unique filename (existing files wont get overwrite)
- SaveAs is now a async-function (include fallback of older saveAs-Functions at options-json
- Save the generated filename to file.stream.filename_write (for getting it to user in Upstream.js)

2nd part for https://github.com/balderdashy/skipper/issues/12 - the other part is in skipper