Closing postponed issues

[JdeH]

The [postponed] issues (issues that we're unlikely to work on soon) are starting to clutter the issue list too much, since by nature they will be on it longer than the rest.

Therefore I will close them, which means they are just moved to "the other category". Since they all share the same label they can easily be retrieved and searched.

If anyone wants to work on a postponed issue, just react on it with a reopen request, and I'll reopen it with the [under construction] label.