Add Jupyter Lab environment

- dependencies used to run the Jupyter Lab environment that are not
  required by the `urban-meal-delivery` package itself are put into
  an installation extra called "research"
- this allows to NOT install the requirements, for example, when
  testing the package in an isolated environment

pyproject.toml

@@ -27,12 +27,30 @@ repository = "https://github.com/webartifex/urban-meal-delivery"
 [tool.poetry.dependencies]
 python = "^3.8"
 
+# Package => code developed in *.py files and packaged under src/urban_meal_delivery
 alembic = "^1.4.2"
 click = "^7.1.2"
 psycopg2 = "^2.8.5"  # adapter for PostgreSQL
 python-dotenv = "^0.14.0"
 sqlalchemy = "^1.3.18"
 
+# Jupyter Lab => notebooks with analyses using the developed package
+# IMPORTANT: must be kept in sync with the "research" extra below
+jupyterlab = { version="^2.2.2", optional=true }
+nb_black = { version="^1.0.7", optional=true }
+numpy = { version="^1.19.1", optional=true }
+pandas = { version="^1.1.0", optional=true }
+pytz = { version="^2020.1", optional=true }
+
+[tool.poetry.extras]
+research = [
+    "jupyterlab",
+    "nb_black",
+    "numpy",
+    "pandas",
+    "pytz",
+]
+
 [tool.poetry.dev-dependencies]
 # Task Runners
 nox = "^2020.5.24"