Luigi Tibaldo / ctools

Remove ctools::time_reference constant and handle the time reference for MET either by using the time reference from the input observation, or by adding a hidden "mjdref" parameter. The following tools transparently use the time reference of the input observation:
* ctselect (apply time reference of each input observation)
* ctbin (apply time reference of first input observation)
* csobsselect (apply time reference of each input observation)

A "mjdref" parameter was added the following tools:
* ctobssim
* cslightcrv
* cspull
* csviscube
* csobsdef

# Conflicts:
#	ChangeLog
#	NEWS
#	doc/source/admin/release_history/1.6.rst

The cstsdist parameter interface is now much simpler, requiring on input either an unbinned, binned or stacked observation. If an observation definition XML file is provided it is assumed that the file only contains event lists.

…TE-END, TIME-OBS and TIME-END

# Conflicts:
#	ChangeLog
#	NEWS
#	doc/source/admin/release_history/1.5.rst

…cripts now from csobservation instead of cslikelihood since they do not use proper optimizers.

The scripts cslightcrv, csphasecrv, cspull, cssens, csspec, cstsdist, and cstsmapsplit now have a "statistics" parameter to allow setting of the optimizer statistic. Except of cstsmapsplit, all of the scripts now derive from the cslikelihood base class.