Plot error when changing the background colour

@salvadord is already working on this.

Since Nov 22, 2022.

When changing the background colour to white, an error appears related to the plots

- "'TypeError' object has no attribute 'plotName'"

```
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
~/git/netpyne-ui/netpyne_ui/netpyne_geppetto.py in getPlot(self, plotName, LFPflavour, theme)
777 else:
--> 778 fig_data = getattr(analysis, plotName)(**args)
779 if isinstance(fig_data, tuple):

~/git/netpyne-ui/src/netpyne/netpyne/analysis/dipole.py in plotDipole(showCell, showPop, timeRange, dpi, figSize, showFig, saveFig)
40
---> 41 p = p/1000.0 # convert from nA to uA
42

TypeError: unsupported operand type(s) for /: 'Dict' and 'float'

During handling of the above exception, another exception occurred:

AttributeError Traceback (most recent call last)
/tmp/ipykernel_212837/2246607073.py in
----> 1 netpyne_geppetto.getPlot(utils.convertToPython('"plotDipole"'),utils.convertToPython('false'),utils.convertToPython('"guiBlack"'))

~/git/netpyne-ui/netpyne_ui/netpyne_geppetto.py in getPlot(self, plotName, LFPflavour, theme)
798 return fig_data
799 except Exception as e:
--> 800 err = "There was an exception in %s():" % (e.plotName)
801 logging.exception(("%s \n %s \n%s" % (err, e, sys.exc_info())))
802

AttributeError: 'TypeError' object has no attribute 'plotName'
```

https://images.zenhubusercontent.com/122103040/dd5cf97f-e3c7-4b37-997c-e9a21346517f/video.mov