Iftach Sadeh / ctools

So far any exception occuring during the construction of the ctools were not catched. This is corrected now.

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

According to a study by Stephan Fegan done in the context of Fermi/LAT analysis, the best way to determine a butterfly diagram is to draw the envelope of the error ellipse of the model parameters. I implemented this method now in ctbutterfly. I also changed the output file, having now two columns giving as function of energy th minimum and maximum intensities.

…gning the old best optimizer result).

… csspec and complemented the copy constructor of cterror (the optimiser was not copied and intialised)