Add tutorial for creating publication-ready images with draw_tree

[edwardchalstrey1]

Issues closed by this PR

• Closes [Tutorial]: How to create publication-ready images of games #732

Description of the changes in this PR

• Upgrades draw_tree to 0.4.0 release
• Adds a new tutorial demonstrating the key functionality of draw_tree when used with pygambit
• Also strips the saved outputs from all the current notebooks for consistency
• Adds "Two-stage matching pennies game" to the catalog from contrib (used in the new tutorial)
• Also tidies the "saving games" sections of tutorials 1&2

How to review this PR

• Look at the new tutorial at https://gambitproject--765.org.readthedocs.build/en/765/tutorials/04_creating_images.html
• See all the tutorials at https://gambitproject--765.org.readthedocs.build/en/765/pygambit.html - some of the images will be different with the new draw_tree version
• Suggest any improvements to draw_tree and whether they need to be made before merging this PR or otherwise can be opened as issues here: https://github.com/gambitproject/draw_tree/issues
  • See the list of the changes in this version of draw_tree: https://github.com/gambitproject/draw_tree/milestone/1?closed=1
• Suggest any changes to how the tutorials are organised or the content of the new one

Note: Since I have stripped the notebook outputs in this PR, the ReviewNB link isn't as useful to look as the rendered docs.

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[edwardchalstrey1]

Going to merge this as Rahul and I discussed on a call last week