Thierry Reposeur / ctools

Added ctool::require_inobs_nocube() method that throws an exception if a counts cube has been specified as inobs parameter. This method is then used by ctbin, ctexpcube, ctpsfcube and ctbkgcube.

… GCTAExposure to GCTACubeExposure and GCTAMeanPsf to GCTACubePsf).

…(see #1360 for details).

…)-function of individual ctools

…d scave() methods to ctool interface. Add read_ahead() method to handle reading of task parameters at the beginning of the task execution. Remove all m_read_ahead members from the derived classes.

…bservation::hasresponse()

The ctbkgcube tool generates a background model for cube-style analysis.

* Checked the code for coding conventions.
* Renamed the angular seperation user parameters to amax and anumbins. "a" stands for angular separation, "d" for delta is less explicit.
* Add ctpsfcube executable unit test