2.7 - Hello, power users

• Advanced settings
  • schema-driven INI editor, 67 keys, searchable reference (sync, jmap, imap, spam, dkim, psl, attachments, compose, db, view)
  • OAuth client secrets never written to advanced.conf - moved to wallet, scrubbed
• Avatars - dead avatarprovider.cpp wired and registered when avatars/enabled, shown in the From row.
• Bug fixes
  • proper context detection: Mark as read / unread, Mark as spam / not spam