Pajamas: New UX architecture

## Problem
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### GitLab is a Gardener
The great George RR Martin once said...
> “I think there are two types of writers, the **architects** and the **gardeners**. The architects plan everything ahead of time, like an architect building a house. They know how many rooms are going to be in the house, what kind of roof they're going to have, where the wires are going to run, what kind of plumbing there's going to be. They have the whole thing designed and blueprinted out before they even nail the first board up. The gardeners dig a hole, drop in a seed and water it. They kind of know what seed it is, they know if planted a fantasy seed or mystery seed or whatever. But as the plant comes up and they water it, they don't know how many branches it's going to have, they find out as it grows. And I'm much more a gardener than an architect.” 

*  **Gardener** - Bottom-up, experimental, opportunistic, looking for emerging structures
*  **Architect** - Top-down, regimented, tightly-controlled, looking to balance the high level with the lower level from the start

I think this mindset can be applied to any creative field (such as design), however, I don't think you necessarily need to be either a `Gardener` or an `Architect`.
**IMO... GitLab is culturally over-indexing on the `Gardener` side of things.**

### The challenge with being a Gardener
Based on my onboarding experience and use of Pajamas, this Gardener mindset has led to a number of pain points...
*  The onboarding experience is scary
*  Design documentation and resources (from my perspective) are quite diffuse across GitLab
*  It's hard to quickly understand what GitLab as a product is - and how it fits together

...There is an opportunity to restructure the experience and content of our Pajamas Design System to ease the onboarding experience and architect content in a more noob-friendly way.

## Solution
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Let's introduce just the right amount of `Architect` into our design system...

I have taken a stab at re-architecting the general experience ([see Pajamas Design System - Architecture Mural](https://app.mural.co/t/gitlab2474/m/gitlab2474/1576610115252/7ba61a8eaf98c494b8d603439d37011757c86b8c?wid=0-1576610284030&outline=open)) - trying to balance a bottom-up *and* top-down approach to a design system. This is WIP and a first iteration of course... I will need input from a broader audience to take into account everything that's important.

See... 
* [Pajamas: Actionable Principles Update](https://gitlab.com/gitlab-org/gitlab-design/issues/797)
* [Pajamas: Define Conceptual Object Model](https://gitlab.com/gitlab-org/gitlab-design/issues/789)

![Screenshot_2019-12-17_at_19.49.56](/uploads/43991241a1584cc752a129b5b3bc4480/Screenshot_2019-12-17_at_19.49.56.png)

With a more balanced approach to PJ's UX architecture, I believe we can...
*  Make onboarding easier through clarity & purpose
*  Simplify the information architecture of http://design.gitlab.com/ 
*  Provide greater context for our lovely components

This is very abstract atm... but I will follow up with how this new type of architectural thinking can benefit the new table and sorting components I am working on.

I would love some feedback! Let me know what you think.

/cc @gitlab-com/gitlab-ux

Story points: 5.0