Consider moving starter site to separate project

## Pros
- Changes to the starter site may be independent of core changes.
- Possibly better handling of multiple starter sites.
## Cons
- Core changes that require starter sites changes require simultaneous releases.
## Possible structure

```
- base/  # all files that are used on all sites
- starter/  # additional files and overrides
- theme1/  # additional files and overrides
...
```
