change the IVA speed text; change speed text only in the atmosphere

Hello Ferram4,

i managed to change the IVA speed text, too. I'm pretty sure that i've squashed all the bugs with it, too. Docking, undocking, switching between vessels, multiple cockpits on one vessel, multiple speedometers in one IVA all seem to be working.

The code is a bit messy with the caching of the references to the speedometers, but it is worthwhile to do it, and it is the best i could come up with. As usual i gave it plenty of comments.

Two other minor things i changed: Speed readout should only be changed when in an atmosphere. 

Second, i changed LateUpdate so only the active FARControlSys would call ChangeSurfVelocity. I guess otherwise it would be called by each ControlSys on the craft. Little bit of optimization.

Cheers,
Michael