active matter tutorial to notebook (#4304)

Fixes #4183 

Description of changes:
- move the active matter tutorial scripts to a single notebook
- add exercise blocks
- rework text

doc/tutorials/active_matter/CMakeLists.txt

@@ -1,23 +1,5 @@
 configure_tutorial_target(
-  TARGET
-  tutorial_am
-  DEPENDS
-  active_matter.ipynb
-  figures/friction.svg
-  figures/pusher-puller.svg
-  figures/enhanced.svg
-  figures/geometry.svg
-  figures/rectify.jpg
-  figures/rectification.svg
-  figures/flow_field.svg
-  exercises/enhanced_diffusion.py
-  exercises/flow_field.py
-  exercises/rectification_geometry.py
-  exercises/rectification_simulation.py
-  solutions/enhanced_diffusion.py
-  solutions/flow_field.py
-  solutions/rectification_geometry.py
-  solutions/rectification_simulation.py
-  solutions/solutions.txt)
+  TARGET tutorial_am DEPENDS active_matter.ipynb figures/friction.svg
+  figures/pusher-puller.svg figures/geometry.svg figures/flow_field.svg)
 
-nb_export(TARGET tutorial_am SUFFIX "" FILE "active_matter.ipynb" HTML_RUN)
+nb_export(TARGET tutorial_am FILE "active_matter.ipynb" HTML_RUN)