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)

site/components/Navbar/NavMenuEntry.tsx

@@ -0,0 +1,51 @@
+import ListItemIcon from "@material-ui/core/ListItemIcon"
+import MenuItem from "@material-ui/core/MenuItem"
+import { SvgIcon, Typography } from "@material-ui/core"
+import { makeStyles } from "@material-ui/core/styles"
+import React from "react"
+
+export interface NavMenuEntryProps {
+  icon: typeof SvgIcon
+  path: string
+  label?: string
+  selected: boolean
+  className?: string
+  onClick?: () => void
+}
+
+export const NavMenuEntry: React.FC<NavMenuEntryProps> = ({
+  className,
+  icon,
+  path,
+  label = path,
+  selected,
+  onClick,
+}) => {
+  const styles = useStyles()
+  const Icon = icon
+  return (
+    <MenuItem selected={selected} className={className} onClick={onClick}>
+      <div className={styles.root}>
+        {icon && (
+          <ListItemIcon>
+            <Icon className={styles.icon} />
+          </ListItemIcon>
+        )}
+        <Typography>{label}</Typography>
+      </div>
+    </MenuItem>
+  )
+}
+
+const useStyles = makeStyles((theme) => ({
+  root: {
+    padding: "2em",
+  },
+  icon: {
+    color: theme.palette.text.primary,
+
+    "& path": {
+      fill: theme.palette.text.primary,
+    },
+  },
+}))