Add no-calibrator reduction capabilities.

For when only target field is observed (i.e. target is also calibrator).

- Update 'write' function to handle 'no-calibrator' obs.
- Added no-cal script. Still need to add flag/logic to use it, though.

Also:
- log full exception stacktraces in reduction script when something goes wrong.
- changed write behaviour to always output UVFITs even if flagging is
  high.