[vtkusers] vtkChartXY

[Hagen Mölle]

Hi Marcus and Eric,

I am finished with writing a new logarithmic scale for logarithmic axis. 
I produced a patch too (git diff > VTK.patch). Is there a specific 
procedure to merge the code into current master of VTK. Before doing 
this you hopefully want to look over the code and test it.

Some remarks to my changes:

1. If axis labels are large then they will overlap.
2. If order of magnitude of the axis is lower than/equal 5 then labels 
will be ... 1 2 5 10 20 50 100 ... Other wise labels will be ... 1 10 
100 1000 ...

Hagen