Iftach Sadeh / ctools

All likelihood ctools now derive from the ctlikelihood base class. This avoids code duplication and provides all likelihood tools with a uniform interface.

(still need to remove some debug statements later)

…)-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.

Still needs to be seen how the error computation can be switched off for recomputation.

GammaLib is undergoing a major interface change which requires adaption of the ctools code.

ctlike now computes the observed number of events and dumps the information just before the predicted number of events into the log file. The difference between the observed and predicted number of events is also given so that one knows immediately if the fit behaved as it should.

This commit closes actions #87 and #88 and the feature #54.

…to understand for the user.

Instead of reading ahead the output parameter, I added a flag that signals when ahead reading is desired.