Benefits:
- Cross browser solution (however only for relatively new browsers)
- Doesn't need extra permission in Chrome
If the browser doesn't suppor the download attribute, then a new tab will
be opened with the exported data.
Other changes:
- Start the download only if the data is not empty (previously the
download started anyway)
- Reorder code in vapi-client.js for Safari, so unnecessary code doesn't
run on extension pages
