GPII-698: Fixed value ranges for speechRate, Volume & fontSize textfield steppers

Basing on value ranges from this document: https://docs.google.com/spreadsheet/ccc?key=0AppduB_JZh5EdGltZnF3dVpKdXcxSVhEZ0VjZGY1U3c&usp=sharing.

Link to JIRA: http://issues.gpii.net/browse/GPII-698