WIP Add private themes

The app is not detected. Can see build logs here: https://dashboard.heroku.com/apps/g5-theme-garden-private/activity

```
Build Log: ID 69aa9c9c-6809-4164-a1d6-bd9eabcc63e7
 -----> Removing .DS_Store files

 !     Push rejected, no Cedar-supported app detected
```