[WIP] Implement open & select file in file manager

(cherry picked from commit 46ad16dea9fac1386d38f747c435744146ac32ac)
Wrap stacktrace output in GitHub MarkDown code tags.

(cherry picked from commit 625cebcaadedb20398276fc808ad39c8d991e89b)
Do not mark articles read if download has failed

This change includes: always try to download unread articles matching ruleset already present in list (aka redownload failed items)

(cherry picked from commit 48a36a381a5d6d87c5b5a358641de807cf80663b)