refactor: Move package.json and other front-end collateral into 'site' (#128)

This refactors the front-end collateral to all live within `site` - so no `package.json` at the root.

The reason we had this initially is that the jest test run and NextJS actually require having _two_ different `tsconfig`s - Next needs `jsx:"preserve"`, while jest needs `jsx:"react"` - we were using `tsconfig`s at different levels at the hierarchy to manage this.

I changed this behavior to still use two different `tsconfig.json`s, which is mandatory - but just side-by-side in `site`.

Once that's fixed, it was easy to move everything into `site`

Follow up from: https://github.com/coder/coder/pull/118#discussion_r796244577

.gitignore

@@ -16,9 +16,12 @@ yarn-error.log
 
 # Front-end ignore
 .next/
+site/.eslintcache
 site/.next/
+site/node_modules/
+site/yarn-error.log
 coverage/
 
 # Build
 bin/
-site/out/
+site/out/