Add support for --no-tty from GPG

I'd like to have a small wrapper in Elisp that allows me to perform signing and encryption actions on an Emacs buffer, however the keybase calls would need to pass on the --no-tty flag to `gpg` - otherwise this error is thrown:

```
gpg: cannot open `/dev/tty': No such device or address
```

It might be possible to extend the GPG wrapper to be able to pass arbitrary options on to GPG so that this could be deferred to "power-users"?

//V

The issue names no files, tests, or entry points. Locate the GPG wrapper and its signing/encryption call path first; confirm completion by exercising those actions without a TTY and checking that --no-tty or a supported arbitrary option reaches gpg without the reported /dev/tty error.

Written by the indexing model from the issue text.