Feature - Multi product documentation

[WouterJanson]

This PR alters the site's structure to support multiple product documentation.
Demo live at: https://wouterjanson.github.io

• Redirects for pages that are moved to the /signhost subdirectory
• Menu's are dynamic based on _data/structure.yaml
• Documentation for Forms is added.

[MrJoe]

Without actually looking closer, but did you make sure all the old links keep working?

[WouterJanson]

Without actually looking closer, but did you make sure all the old links keep working?

I have tested links such as /postback those go to the appropriate page in the sub directory.
However the / currently doesn't go to /singhost but to a landing page with the separate products instead. But we could choose to drop this page, and make /signhost the default.

[WouterJanson]

Hash paramaters won't work unfortunately, but the user is taken to the correct page.