Disable running remote Closure by default

I recognize the appeal of "works by default", but I think "privacy by default" is favorable here, so I've changed the default behavior to this:

```console
sirian@Mollari forml$ forml -t readme.forml
[*] Loading readme.forml
[*] Compiling readme.obj 
[X] Closure readme.js 
Local Closure unavailable; pass -remote option to use public server
```

Simply follow the advice in the error message to get back the old behavior.

The parent commit also contains some error messages &c for the Closure functions, if you'd prefer to merge only that.