GammaLib

I would like to add GCTAPsfMap class to handle psf in the format of (energy,skycoordinate). This is useful for averaged analysis. In averaged analysis, run informations are missing. Parameters like offset, azimuth angle and zenith can’t be calculated. To handle multiple sources in fov. I propose building a new class GCTAPsfMap to handle averaged pdf for sky directions. A proposed header file for this class is attached. The main problem I see is
- We have to add corresponding virtual methods in GCTAPsf and GCTAResponse.
- We need 3D interpolation. This is not really needed because to interpolate skyx,skyy is not really necessary. We can just take the closes skyx,skyy nodes.

Are there other problems?