Update ProcessCcdTask so that it can be used with different datasete types as appropriate for the ISR task. This will allow us to get rid of obs-specific variants ProcessCcdSdssTask and ProcessCcdDecamTask

The plan is to change ProcessCcdTask as follows:

• set doMakeDataRefList=False in the call to add_id_argument
• get the dataset type from the ISR task (default to "raw") and set it in data container
• make the dataRef list by calling makeDataRefList on the data container

Question for DECam folks: do you want two executable scripts for DECam (one that processes data from the community pipeline and one that performs ISR)? Or do you prefer one exectutable (in which case you switch between performing ISR and reading the output of the community pipeline output by retargeting the ISR task)? If you prefer one binary, then which should be the default: perform ISR or read the output of the community pipeline?