application website validation, don't link to app website if website isn't set,
also comment out animated boost icon from #464 until it's consistent with non-animated version

with YAML-defined defaults. Add admin page for editing global settings. Add "site_description"
setting that would show as a paragraph on the frontpage

fix bug in process feed service

Deduplicating some logic and switching to pluck, to avoid pulling the entire model in memory.

h-feed, h-card and h-entry

for local attachments, use them in URLs. Check status privacy
before redirecting to actual file.