Isolate state clearing to just the registry and add more comments

Author: ned2

Diff for: dash/dash.py

@@ -173,7 +173,13 @@ def _get_skip(text, divider=2):
 def init_dash_globals():
     """Ensure that all Dash global state is re-initialised."""
     _pages.PAGE_REGISTRY.clear()
-    _pages.CONFIG.clear()
+
+    # this line of thinking could be extended to potentially clear the following:
+    # _pages.CONFIG
+    # _get_paths.CONFIG
+    # _callback.GLOBAL_CALLBACK_MAP
+    # _callback.GLOBAL_CALLBACK_LIST
+    # _callback.GLOBAL_INLINE_SCRIPTS
 
 
 # pylint: disable=too-many-instance-attributes