Help widget

[beganovich]

This adds a tiny help widget on the right side of the screen with some preprocessing. It's kept on screen even when clicking outside so you don't have to fight with it. It will stay open, you can scroll, follow the guide and use the app in the "background".

• Relative assets URLs are swapped
• <x-next> is gone
• Any layout metadata is gone

We can directly point the URL to the documentation as a source.

<HelpWidget
  id="import-and-export"
  url="https://raw.githubusercontent.com/invoiceninja/invoiceninja.github..."
/>