Consolidate all environments in one section

Some of these names relate to specific tools, others could be used by multiple tools. In particular, virtualenv, the most popular tool for creating Python environments, does not mandate any of these and venv/ or .venv are simply conventional. It is more readable to group all of these together.

Python.gitignore

@@ -8,7 +8,6 @@ __pycache__/
 
 # Distribution / packaging
 .Python
-env/
 build/
 develop-eggs/
 dist/
@@ -79,11 +78,10 @@ celerybeat-schedule
 # SageMath parsed files
 *.sage.py
 
-# dotenv
+# Environments
 .env
-
-# virtualenv
 .venv
+env/
 venv/
 ENV/