Feature/url revisionless

- [x] Ready for merge

Implementation for #1232.

TODO:

- [x] Add UI for selecting snapshots (dropdown next to snapshot radio)
- [x] Ensure sharing latest bin updates url to non-snapshot
- [x] Ensure sharing non-latest remains on url
- [x] Ensure "share" menu shows correct url (in link and embed) - when on latest, there should be no snapshot number
- [x] Ensure sharing a snapshot and visiting snapshot, remains on snapshot link
- [x] Ensure ALL bins, if not owner, clone
- [x] ~~Ensure share menu shows the current snapshot, and the maximum snapshot~~
- [x] If user opens latest in another tab or window *and edits* automatically create a snapshot in the first window
- [x] Snapshots should have the number in the title (#n) and number in url.
- [x] Link to direct sources of bin
- [x] If viewing the latest bin - but don't have write permission, the share box should be on snapshot and url should remain on snapshot
- [x] Fix #1537
- [x] If no sources, hide "sources"

Issues:

Q: What if it's an anonymous bin, and you don't own the latest revision (though in future you will)?
A: The share panel shouldn't let you select latest and live without it causing a clone event. @dannyhope  would like a +1 or -1 on this)

Deferred: 


- [ ] Ensure anonymous users are correctly identified as owner of previous bins
- [ ] If possible, allow anonymous users to continue to create revisions on old bins they "once" created.
- [ ] Ensure delete, deletes *all* snapshots