Add option to show block if menu tree contains no links

Ran out of time to test and commit this so moving to the next release plan

Here I leave a patch compatible with 8.x-1.11

I think this is likely a duplicate of some of the other issues mentioned... can someone confirm?

I am going to commit this, to get the feature in, it's been ages on the burner and obviously people want it.

Thanks, everyone, for your work on this and for your patience!

Automatically closed - issue fixed for 2 weeks with no activity.