Alexander Ziegler / 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.

The GCTAEventCube::map() method has been renamed to GCTAEventCube::counts() (#1789)

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

Although the get_obs() method was put back, ctmodel used the dummy cube (which consisted of a single pixel) instead of a cube defined from the input parameters. This was due to an internal change of the logic, that now has been corrected for.

Without the energy margin, roundoff errors may lead to the exclusion of the energy bin in case that a single energy bin is used.

…d in observation ebounds. Also added some improvements to csspec.

…lso modified consistently, csresmap can now also take two maps (cnt and model) as input and compute the residuals directly. The algorithm parameter has been made unhidden

Conflicts:
	ChangeLog
	NEWS
	src/ctbkgcube/ctbkgcube.cpp
	test/test_ctools.sh