Improvements in documentations and new AEV features class.

- docs.sources.docs:
    * More modules are mocked for correct rendering on the rdt website.

- atomistic.features.gaussian:
    * Changes to make the class compatible with AEV.
    * Change to f-strings.

- atomistic.features.aev:
    * New AEV addition class.
    * It just computes G2 symmetry functions.

- atomistic.modules.neuralnetwork:
    * When collecting the activations we create leaf variables.

docs/source/conf.py

@@ -49,7 +49,11 @@ def __getattr__(cls, name):
         "dscribe",
         "msgpack_python",
         "scikit_learn",
-        "dask"
+        "dask", 
+        "ase.neighborlist", 
+        "plotly.express", 
+        "ase.calculators", 
+        "ase.io"
     ]
 
     sys.modules.update((mod_name, Mock()) for mod_name in MOCK_MODULES)
@@ -152,7 +156,7 @@ def __getattr__(cls, name):
 # -- Options for HTMLHelp output ---------------------------------------------
 
 # Output file base name for HTML help builder.
-htmlhelp_basename = "ML4Chemdoc"
+htmlhelp_basename = "ML4Chem"
 
 
 # -- Options for LaTeX output ------------------------------------------------