Add test data for diffuse emission analysis in the Crab region.
Updated link for feature request submission.
Add pixel value set operator=.

The pixel value set operator will assign the same value to all sky map pixels, i.e.

map = 1.0;

will set all map pixels to 1.0.
Add GCTASourceCubeDiffuse class and start implementing the GCTAResponseCube::irf_diffuse method.

The actual implementation of the IRF computation in GCTAResponseCube::irf_diffuse is still missing, yet we have the structure in place that allows not handling of the diffuse response cubes. We essentially need now a method that computes the diffuse IRF for a given event.
Implemented diffuse source cube PSF integration.

Now, the diffuse source cube class is fully functional. Some tests were done to adjust the integration precision.