GPII-722: Fixing problem with blank sentences.

http://issues.gpii.net/browse/GPII-722
Many screen readers (like NVDA and JAWS) pronounce blank when an empty span is found. The above "gpiic-prefsEditor-messageLine" span will obtain text when the user presses the "save and apply" button. So, we hide the span and show it only after the button is pressed.