URL improvements

[franzaps]

• Autodetect URL from current address (so anchor should not be required)
• Allow multiple URLs to be passed to the anchor prop (useful for similar domains representing the same resource such as, example: youtube.com, youtu.be, m.youtube.com)
• Should we add all root replies as anchor events and retrieve with #r? This would prevent having to create a "Comments on https://franzap.com/test.html (added by zapthreads) " event

[franzaps]

Change to "I just opened a comments thread on https://franzap.com/test.html"