add wrappe for getBoxFilter
add "getCustomPosition"

integrate fluid particle trajectories in filtered fields
speed up "refine_grid"

I'm now using correlate1d from scipy.ndimage.filters, which is not a big
deal as a new dependency, since scipy is very likely to be present
anyway.
apparently, things are happening much faster now.
add getThreshold wrapper
add time information to isotropic1024coarse
add thresholding ui example
Merge branch 'feature-thresholding' into develop
generalize get_big_cutout

i.e. make the call consistent with get_cutout, and it can now be used
for general shapes of the data.
make test consistent with new get_big_cutout
Merge branch 'develop'