app: Fix message decoding in client
app: Fix message decoding in client

In previous refactorings, the decoding of messages got broken because
calling #toString for JString results to "JString(value)", instead of
just the value.

Signed-off-by: Aki Saarinen <2c8035bb80cf98a391872dcbe797b269d759f6d9@reaktor.fi>

akisaarinen/ccf,akisaarinen/ccf