Iftach Sadeh / 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:
#	src/ctselect/ctselect.par

The ctool::get_roi() replaces some duplicated code in ctselect and ctcubemask. The method extracts the RoI from the user parameters "ra", "dec" and "rad". In case the "usepnt" parameter is present and set to "yes", the "ra" and "dec" parameters will not be read, and it's up to the client to set the RoI centre properly.

…)-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.

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

The usepnt parameter now signals when the pointing should be used as ROI centre. This allows arbitrary values for ra/dec (before, ra=0 and dec=0 signalled that the pointing should be used).

The tool now uses the new GTime interface. In particular, the input time is now given in CTA reference time in seconds.

Filenames are now always accessed using the filename() method so that environment variables get correctly expanded.

The prefix is now accessed using the string() method instead of the generic value() method, so that string checkings can be performed.

…to understand for the user.

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

…rocessing collections of event lists with a single ctselect run.

…ointing as ROI centre