Update setup.md, add to navigation, remove whatsnew and vision

This is still a WIP. Do not merge.

This PR introduces mange of the discussed changes and some news I felt made sense.

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This is the new flow:

- Welcome
    - Links to the Goodie Quickstart if they're interested
        - This will have them run through the Setup (we're now duplicating this text, not ideal...)
        - ...and then create a simple Goodie, they have the option to submit it through a PR
        - Then they should go back to the start of the docs to Determine IA Type for their next IA
    - Otherwise, tells them to Determine IA Type
- Determine IA Type
    - They figure out their IA type (no longer fork from here)
- Setup Dev Environment
    - Now they setup their env, we highly suggest Codio, mention local option, then walk them through the process where they:
        - Get a GitHub account
        - Get a Codio Account
        - Clone the Codio Box
        - Fork the repo (links back to Determine IA Type in case)
        - Are directed to the Overview for their IA Type in the Docs

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The "What's New" page has been removed and so has the "Vision".

//cc @zekiel @jkanarek 
:+1: