Created Velocity Factors, Changed Default Factor

Created velocity radio buttons.
Velocity radio buttons now change the speed factor.
Changed default factor to 100 for fast. The turtlebot now goes fast when
travelling forwards, so that's a plus.
Medium factor is 50 and slow is 20. However these factors go slow when
going forwards, and fast when going backwards. We will need to do more
testing to find the right factors.