Ability to link nodes

Just to second Michael Rupp's comment on the nextcloud store, pasted in below.

It would be really helpful for me to be able to link two nodes. That is a must have feature for me. Ill follow the new versions and hope it will be implemented soon. Because otherwise the app is good looking, easy to use, I'd love to use it.

Original comment with a lot of nice to haves...

I kind of like it. Fairly easy to guess how to use most features. Nice built-in formatting options.

I was disappointed that I can't have 2 main nodes on a single map. Some mind map programs allow the user to post all the concepts prior to any linking. I would have liked to do that with my first map.

I was disappointed that I can't make more than one link. For example, the child of one node is also the child of another node. I had to create an identical child node to represent it, but that's not appropriate because it represents twin children instead of a single child with two parents.

I was disappointed that a sibling node looked identical to a child node in the graphical representation. Seems like it should have had a different connector and been the same formatting as the initial node that it was a sibling from.

It would be cool if the links were adjustable in a way that they could show arrows, or represent a bi-directional flow, or dashed vs solid lines.

Anyway, thanks for making this. It's a cool app.

No files, tests, or entry points are named in the issue. Start by locating the JavaScript code for the map and node relationships, then clarify the intended linking behavior and its acceptance criteria before estimating the work.