(Bug 4239) Mark deleted crosspost accounts as inactive

Keep the metadata (sans sensitive info), so that we don't break
importing, and we can maybe adjust the crosspost link display settings
later on.

Also adjusts the places where we load the External/Account info so that
we fetch the active status, and filter to only show active accounts in
most cases
Merge pull request #244 from afuna/externalaccount-delete-bug4861

(Bug 4239) Mark deleted crosspost accounts as inactive