Added feature to export/import menus!

[yar2000T]

No description provided.

[Schneegans]

This looks quite good now! I think there are two things which we could improve:

1. I think you could remove the showSaveDialog and showErrorDialog from the settings API. Simply put all this logic in the settings-window.export-menu and settings-window.import-menu handlers respectively. This would safe us some round trips between the processes and would make the code easier to read, I think.
2. The error message if an invalid JSON is imported is really hard to read. Can this be improved somehow?

[yar2000T]

I dont know what we can do abot redability of errors, I changed layout of error window and applied your 1 suggestion