feat(cdr): Initial UI scaffolding

This is testing out [Approach 3](https://www.notion.so/coderhq/Workspaces-v2-Initial-UI-Scaffolding-3b07d2847eed48839a7e6f0f2bb9bf56#56256f25d2954897a8ee315f0820cedd) in the UI scaffolding RFC.

Fixes https://github.com/coder/coder/issues/11

The folder structure looks like:
- `site`
    - `components` (buttons, empty state, etc)
    - `pages` (large sections of UI -> composition of components)
    - `theme` (files defining our palette)

Several components were able to be brought in essentially unmodified:
- `SplitButton`
- `EmptyState`
- `Footer`
-  All the icons / logos
- Theming (removed several items that aren't necessary, yet, though)

Other components had more coupling, and need more refactoring:
- `NavBar`
- `Confetti`

Current State:

![2022-01-06 17 16 31](https://user-images.githubusercontent.com/88213859/148475521-96e080cc-1d33-4b8e-a434-29e388936e3f.gif)

For a full working app, there's potentially a lot more to bring in:
- User / Account Settings Stuff
- Users Page
- Organizations Page
(and all the supporting dependencies)

README.md

@@ -11,6 +11,7 @@ This repository contains source code for Coder V2. Additional documentation:
 
 - `.github/`: Settings for [Dependabot for updating dependencies](https://docs.github.com/en/code-security/supply-chain-security/customizing-dependency-updates) and [build/deploy pipelines with GitHub Actions](https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions).
   - [`semantic.yaml`](./github/semantic.yaml): Configuration for [semantic pull requests](https://github.com/apps/semantic-pull-requests)
+- `site`: Front-end UI code.
 
 ## Front-End Plan