Merge tkinterpp-notebook into tkinterpp-merger to add Notebook widget

[sbordeyne]

PR Details:

• Widget name: Notebook
• Author: Dogeek (based on @j4321 's work)

Description

A Notebook widget that includes functionnality to close and reorder tabs

Checklist

• Widget in a separate file in the appropriate folder
• Widget functions properly on both Windows and Linux
• Widget code includes docstrings with parameter descriptions
• Included an example file in /examples
• Widget is covered by unitttests in /tests
• Widget includes required assets files
• Reference to widget in AUTHORS.md
• Entry in sphinx documentation

[sbordeyne]

Largely based on your work @j4321 , but I'm also working on integrating "drag to new toplevel" functionality", as well as adding traversal with the mousewheel when hovering the tab row.

[j4321]

In addition to my comments on specific lines, there are still some issues with the style. Especially, when I execute setup_style() after creating the notebook, I get (even running directly the example without using any interactive console)

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/media/DATA/Divers/ttkwidgets/ttkwidgets/notebook.py", line 388, in setup_style
    style.element_create('close', 'image', "img_close",
  File "/usr/lib/python3.8/tkinter/ttk.py", line 465, in element_create
    self.tk.call(self._name, "element", "create", elementname, etype,
_tkinter.TclError: image "img_close" doesn't exist

Also the widget does not adapt totally to changes of theme after its creation, an feature I had not worked on in my app since the theme was chosen once and for all.

Finally, with some themes (e.g. 'clam' and 'alt') the tabs don't have visible borders. This seems to come from l. 424

style.configure('Notebook.Tab', relief='raised', borderwidth=1,
                        **style_config)

from the style_config, however I don't understand why since the default lightcolor and darkcolor are different. I can help you look into it.

[sbordeyne]

A number of these should be fixed now