Allow customizing the position of ray start speed

[agronick]

One of my users had commented that they didn't like that the ray speedometer drew from the beginning of the gauge instead of at 0. This looked strange especially when it was an arbitrary negative number. I added an option to set a start value. I left the current functionality but you can now set app:sv_rayStartSpeed="0" to draw from 0 and it will draw backwards if the value is less than 0.

You can see how it looks when starting from 0 instead of the minimum value.