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
