Reference correct profile fields in CSV export

Reference the proper profile fields for user notification settings
that were changed as requested in #811.

This is a regression introducted by
05c54cc587f113b37ed188c77d55a68297fe22cf.

Closes #859
Update default summary copy

Update default summary copy that shows up as a placeholder in the
builder so it encourages shorter (< 250 character) summaries.

Closes #858
Support oEmbeding instagram.com URLs

Previously, only instagra.am URLs were matched by the regex used
to set up Instagram as a provider with micawber.

Closes #860