Corrected coordinate computation in drawing a sphere/disk. Now centering also working when box has negative origin. Replaced DrawCircle.hpp by DrawDisk.hpp, because name circle misleading.

Update to current state of master.

Deleted file GaussFilter.hpp. No longer needed. Problem with this form of gauss filter: weights do not exactly sum up to 1 due to rounding errors.

Deleted lines related to Gauss smoothing. The way the Gauss smoothing was done created problems, because the weights were not adding up to exactly 1 but had a round off error. Also Gauss smoothing is not really needed prior to the redistancing.