Improve error handling of ee site create

The following error message should be improved:
```
ee site create example.com --mu=subdom
Error: Parameter errors:
unknown --mu parameter
```

A good error message would be:
```
ee site create example.com --mu=subdom
Error: found --mu parameter in `wp` site type. Perhaps you forgot to add `--type=wp`?
```

Although this will involve a non-trivial amount of work, It'll really improve UX of EE.