Currently translated at 100.0% (729 of 729 strings)

Translation: Tiny Tiny RSS/messages
Translate-URL: https://weblate.tt-rss.org/projects/tt-rss/messages/de/

 * draw a basic form for testurl() if no url is given
 * only process specific JSON media files/child elements until something is found
 * handle generic preview images for self posts (not link posts because
link is handled afterwards)

add a hack (Headlines.unpackVisible) to workaround against unpack observer sometimes missing articles

- remove code to manually archive/unarchive articles
- remove ttrss_archived_feeds/orig_feed_id handling - the whole thing was implemented for
this data to be kept indefinitely; it doesn't make a lot of sense to deal with this stuff
now that it is expired after one month anyway (same reasons as feed browser being removed - privacy)
- remove "originally from"-related stuff because of the above
- also remove unused remaining frontend/backend code related to feed browser (rip)

PluginHost: add HOOK_HEADLINE_TOOLBAR_SELECT_MENU_ITEM
Headlines.onActionChanged: removed