change the clipping distance after registration

[jonny.pye]

I have noticed if the clipping distance is left at a high number (180m default) and you only have a small scan set then you can end up with a huge limit box when you reset it. It doesn't seem to effect anything else but gets kind of annoying when you have to keep resizing from a distance when you want to focus on a small part of the scan and save a view state. 

It would be great to be able to change what you have left the clipping distance as afterwards so the limit box doesn't reset to a large distance from your actual scan.