Halve the size of auto-generated event IDs.

Use simpleflake (64 bits) instead of UUID1 (128 bits) and base36 instead
of base32 encoding.
Remove orphaned separators when an update is removed.
Get rid of left-margin on edit buttons in narrow screen mode.
Only replace standalone links with embeds.

The scraper code will only process links in their own paragraph.
However, the JS would replace any link with the correct URL with the
embed. This meant that if the URL for an embedded resource were also
linked in a paragraph of explanitory text, it'd get replaced
unexpectedly with the embed.
Fall back to Embedly Cards when no other embeds happen.

This allows for static images, news articles, etc.