Projection of particle shape on a rotated grid

[GoogleCodeExporter]

Currently, rotation of the particle is emulated by inverse rotation of 
everything else. This is proper way to do for free space. However, when 
particle is near a surface(issue 101), the surface determines the grid 
orientation (to be compatible with FFT acceleration). So there is no simple way 
to simulate, e.g., a cube which is not parallel to the plane.

This issue is about a "filter", which will rotate the predefined (or read from 
file) particle shape and project it onto an original grid (oriented with 
respect to the laboratory reference frame).

To test this filter, one may use it in free space and compare with currently 
used emulation. The differences should be minor, and decrease with increasing 
number of dipoles (for fixed particle).

This will also help for more general implementation of periodic particles 
(issue 85), e.g. enable periodicity that is not along the main (most simple) 
particle axes.

Original issue reported on code.google.com by yurkin on 9 Aug 2013 at 12:43

[myurkin]

#101 #85

[myurkin]

This will also help with the WKB field as a first guess for the iterative solver (#59) - now it is only possible for propagation along the z-axis.