FunctionSignature, functionArgumentsSignature: use string not stream, cache result.
FunctionSignature, functionArgumentsSignature: use string not stream, cache result.

Change-Id: Ia596735faa6d900711cb71841bea21869c059d42

vbarbaresi/libqi,aldebaran/libqi-java,aldebaran/libqi,aldebaran/libqi,aldebaran/libqi-java,aldebaran/libqi,aldebaran/libqi-java,bsautron/libqi