Restructure into IOTA, Shimmer, and Next

[jlvandenhout]

trafficstars

This is a tracking issue for the restructure and separation into IOTA-, Shimmer-, and Next-specific environments. This will allow:

• A separate landing page, navbar, and theme per environment:
  • #631
  • #691
  • #693
  • #709
• A more clear indication of what content and what versions of projects belong to which environments:
  • #631
  • #692
• A more logical navigational structure and reduction in content:
  • #660
  • #694
  • #709
  • #710

Questions:

1. Should we remove FAQ's under about? It's just an aggregator.
2. Now that we have the iota-wiki organization, should we have a separate tutorial repo?

Related TODOs:

• [ ] Relocate blog to its own repo.
• [ ] Relocate media library to its own repo.
• [ ] Remove Future after split.
• [ ] Remove Networks after split.

Restructure TODOs:

• [x] Create two directories under content directory: iota, and common.
• [x] Replicate new and applicable structure under each environment directory for internal documentation.
• [x] Add an external directory to each environment. Any applicable external documentation, and associated versions, will be located here as submodules.
• [ ] Remove any remaining content from the repo.
• [x] Update sidebars.js files to represent new structure.
• [x] Update package.json and docusaurus.config.js files to represent new structure.
• [x] Update navbar configuration to new structure.
• [x] Copy iota directory content to shimmer and next.
• [x] Update shimmer and next to represent their applicable states.

[Dr-Electron]

Ser. This is out of date :trollface: