Restructure plotframes.py

[armengau]

@weaverba137 I'd like now to restructure essentially the plotframes.py code in a new branch. On the other hand plotspecutils is largely redundant with plotframes. Does it make sense to fully merge both or do you want to keep them separate?
What do you think of the following:

1. Maybe first merge plotspecutils with plotframes? Looking at their diff, it looks easy. Maybe also find a different name: in the end, external users or scripts use eg "from prospect import MODULE" then "MODULE.plotspectra()".
   Well, for this first step I'm not sure what to do.

2. Create few classes, one file/class, containing the main data in plotframes.plotspectra(). Once this is done, plotframes.plotspectra() should have a reasonable nb of code lines. Suggested classes, with the associated most important data:

• class ProspectCDS:
  cds_spectra
  cds_model
  cds_targetinfo
• class ProspectPlotSet:
  fig
  data_lines
  noise_lines
  model_lines
  zoomfig
  imfig
  emission/absorption lines (should be renamed)
• class ProspectWidgetSet:
  ifiberslider (could we rename it to ispectrumslider ?)
  smootherslider
  prev/next_button
  several z widgets
  target info display
  several VI widgets (may be an independent class)

3. Move remaining functions in plotframes.py to separate files (eg one file for emission/abs line functions).
   I don't know what to do with the main. I would remove it entirely (there's no main in plotspecutils).

4. Remove unused functions in utilities.py

Originally posted by @armengau in #49 (comment)

[weaverba137]

Reopening an issue basically means that the original issue was not fixed or that a code regression has caused a bug to reappear. In #49, a lot of it was fixed, and it is more appropriate to open individual issues on each of the remaining tasks. In fact, this issue itself could have been factored into 4 separate issues.

I will start by taking a look at the diff between plotframes.py and plotspecutils.py.

[armengau]

The main restructure was done in #67.

I still leave this open until utilities.py is cleaned.

[weaverba137]

@armengau, Presumably this was fixed by #73?

[armengau]

Fixed by #73