Support for translations of menu items

I had also some problems with the previous patch using the UI (Warning: Illegal string offset 'menu_name') and the safe import, so here is an updated patch that Works for me™ ^^

Thank you for the work on this.

A small change to support Translatable menu link uri → module through the link_override field.

This way you can translate the URI and it will be exported to.

Having this feature for the 2.0.x version of the module would be a blessing. I have a large menu that needs translating and this would be a tremendous help.

To make this easier to review, I've created a merge request. The patch didn't apply properly, so I tried to re-create it, but I may have made a mistake in doing so: please ensure that the changes in the merge request fixes the problem and report back here.

Note that this is a patch to an unsupported branch (8.x-1.x). I haven't yet had a chance to determine if this issue is still present in the 2.x branch, nor if this patch would also apply there; @elkaro, do you know if it is still an issue in the 2.x branch?

Marking as "Maintainer Needs More Info", awaiting a response to the question in #16.