MacOS: access to logo file denied

[iaik-jheher]

MacOS security features prevent programmatic access to files in a variety of "secure" locations unless those files have previously been chosen by user gesture (e.g., drag/drop, or the "open" dialog.) This prevents us from loading a chosen custom emblem if it is in such a secure location, such as the "Documents" folder.

We already cache a scaled version of the custom emblem in the configuration directory. We should re-evaluate why we even store the path of/access the original.

(internal note: cf. original email report, Feb 6th)