Wrijupan Bhattacharyya / ctools

The publish parameter has been added to the following tools:
- ctbin
- ctbkgcube
- ctcubemask
- ctexpcube
- ctmodel
- ctskymap
- cttsmap

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.

…(see #1360 for details).

…)-function of individual ctools

…odel with a standard diffuse cube background model that can be used for stacked analysis. The model container can be either retrieved using the models() method, or it can be written to disk with the save() method.

…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.

…ovided by the base class

The background models are now livetime weighted before addition, and only event bins are filled that fall within the RoI of the corresponding event list.

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