Improved Performance Widget by creating less String objects logging only...

... once per second.

The String constructor "+" creates 3(if I remember correctly) String objects. 
This can call Dalvik GC quite ofter in Android if it's called 60 times per second in different places.

This commit changes the times setText() method it's invoked from 60 times per second to 1. 
Plus the FPS can only change once every second.