Switching languages doesn't copy already provided input and output

IMO, using the current output as the new query would greatly improve UX.

Instead of `https://beta.apertium.org/#?dir=spa-eng&q=Buenos%20Muchacho`
to `https://beta.apertium.org/#?dir=eng-spa&q=Buenos%20Muchacho`, 

`https://beta.apertium.org/#?dir=spa-eng&q=Buenos%20Muchacho` to `https://beta.apertium.org/#?dir=eng-spa&q=Good%20Boy`?