VHRatio ambiguous for vertical kicker

[Laurie Nevay]

vhRatio implies vertical : horizontal ratio for each object. In the case of a vkicker this is rotated so it's really hvratio.

Either fix or explain clearly in manual.

[Laurie Nevay]

I have revised the implementation to use outerDiameter and vhRatio consistently for vkickers so they are the same as any other magnet. outerDiameter always refers to the horizontal size and vhRatio the vertical to horizontal ratio in the lab frame.

outerDiameter will be rename (in a backwards compatible way) to horizontalWidth to be clearer.