Wrijupan Bhattacharyya / ctools

…ag in the execute() method.

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.

…in case that those are not provided in the event list.

…(see #1360 for details).

…)-function of individual ctools

…s. This method is useful for debugging the memory usage of 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.

…esponse for all CTA observation in the container that have not yet a response using the task parameters.

…ss for CTA observation response setting.

The ctool base class is now used in the ctbin tool. The get_ebounds() method has been moved to the ctool base class so that it can be used also in other tools. This reduces code duplication.