Improve plotting docs

This MR ...

updates the Utopia/utopya plotting docs:

• Restructures the usage/eval section
• Adds articles on:
  • line plots
  • stacked lines and facet grids
  • 2D & 3D scatter plots
  • heatmaps
  • histograms
  • DAG operations
  • Base plots
  • Plotting subspaces
  • Plot sweeps
• Modifies the existing articles on
  • animations
  • graphs
  • adjusting the plot styles
  • custom DAG operations
• Reduces usage of 'dummy' configs, instead drawing examples from configurations of real Utopia models (SEIRD/Opinionet)
• Adds example plots from real Utopia models, automatically generated by the CI
• Adds a summary to the beginning of each article
• Updates references to the use of the ColorManager
• Uses the current state-of-the-art dantro base plots
• Reduces the focus on differentiating between universe and multiverse plots
• Writes articles in the style of a tutorial; each page should be independently readable, but with references to other pages where appropriate
• Links to dantro docs on the DAG and base plots.

Also makes some minor improvements elsewhere:

• Fixes a broken link to the SimpleFlocking model
• Uses the .plot.facet_grid.scatter function for SEIRD phase diagrams and removes the old python plotting function
• Uses the @is_operation decorator for Opinionet plots

Can this MR be accepted?

• Docs reviewed and checked by @tgaskin
• Plots checked
• Example configs checked
• Pipeline passing without warnings
• History cleaned up
• Reviewed and approved by @blsqr

Related #259