Do not crash when startup up without network access
Detect plugins that return FALSE and do not set an error

Also, split up the method so that we don't leak a small string on failure.
Only set up the SoupSession in fedora-tagger when required

This does not need to be done before showing the UI.
Notify about the correct application when installing from the details panel

If the user switches the details view to another application, we have to notify
about the thing we're installing, not the new application we're showing.

Resolves: https://bugzilla.gnome.org/show_bug.cgi?id=710192