Need more user friendly error messages in quick look scripts.

[StuartLittlefair]

The error message raised when scripts such as nrtplot and reduce cannot crop a calibration file to match the data are not really that clear, and that has led to at least one instance of a fault report at the GTC.

29, utc= 2000-01-01 00:00:29.000 (nok), Traceback (most recent call last):                    
  File "/usr/local/python-3.11.4/bin/nrtplot", line 7, in <module>                            
    sys.exit(nrtplot())                                                                       
             ^^^^^^^^^                                                                        
  File "/usr/local/python-3.11.4/lib/python3.11/site-packages/hipercam/scripts/nrtplot.py     ", line 885, in nrtplot                                                                       
    bias = bias.crop(mccd)
           ^^^^^^^^^^^^^^^
  File "/usr/local/python-3.11.4/lib/python3.11/site-packages/hipercam/ccd.py", line 796, in crop
    tmccd[cnam] = self[cnam].crop(ccd)
                  ^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/python-3.11.4/lib/python3.11/site-packages/hipercam/ccd.py", line 553, in crop
    raise HipercamError(
hipercam.core.HipercamError: failed to find any enclosing window for window label = E1

We should make these error messages more user friendly.