Move docs to hugo (with proper git history)

[benolayinka]

This PR migrates the current TTN.org/learn section to Hugo, with the following content sections from the ttn.org restructuring:

• Applications
• Devices
• LoraWAN
• V2 Docs
• Quick Start

Subsections of LoRaWAN will be:

• Glossary
• LoRaWAN specifications
• LoRaWAN fundamentals

Currently looks like this:

[nejraselimovic]

To me, this looks really good, only thing I don't like are these page cards. I would remove those completely, the left navigation seems enough for me, but let's see what @laurensslats thinks

[benolayinka]

To me, this looks really good, only thing I don't like are these page cards. I would remove those completely, the left navigation seems enough for me, but let's see what @laurensslats thinks

I removed them at first, but it makes pages with little content very empty, and some people probably like to navigate within the page.

[michalborkowski96]

We've tested this, so I guess it's fine. Except for old links though, that still needs to be tested. When we're ready, we need to synchronize and deploy our changes at the same time.