DiscreteXrayTransform does not use weighting properly

[kohr-h]

The current implementation of the DiscreteXrayTransform operator initializes a DiscreteLp for its range from the given geometry, however without using proper weighing. This should be fixed.

[kohr-h]

I should add that this refers to a branch. The exact location of the bug is here. The space initializer should use geometry.grid.cell_volume() as weight.

This is only a temporary fix, we need to have a closer look on the desired structure of the range.

[adler-j]

This should be fixed now, correct?

[kohr-h]

It is indeed, but still on a branch, so technically it's still open. But since there is no bug on master, let's say it's fixed. We should, however, open a new one regarding non-uniform sampling of the angles and the weights which follow from that. It's not supported yet.