make*Signature: Replace stringstream by string.
make*Signature: Replace stringstream by string.

Faster.

Change-Id: If5c630e624e9d6e5a3ba02cdb15bdc5a33ac7cba
Reviewed-on: http://gerrit.aldebaran.lan:8080/18979
Reviewed-by: cgestes <ddb78fe00abb42f91254c16a0860e38eb0781789@aldebaran-robotics.com>
Reviewed-by: mnottale <e3ccf1b6558404e921a21fa09cebb1153b50ec36@aldebaran-robotics.com>
Tested-by: mnottale <e3ccf1b6558404e921a21fa09cebb1153b50ec36@aldebaran-robotics.com>

aldebaran/libqi,vbarbaresi/libqi,aldebaran/libqi,bsautron/libqi,aldebaran/libqi