Multiple files import at once

Issue description

It would be nice if we could import a set of structure files instead of one at a time. I made a few structures in different files and then had to import them one by one. it would be faster if we could do it all at once.

Issue comments

I have renamed this ticket to make it universal, as this would be a nice feature for all file importers.

The second part does not make much sense, as you can remove the structure and import it again.

You are right the update structure file button is redundant. I have updated it to reflect this.