Use entrypoints for app registration

pyproject.toml

@@ -47,6 +47,13 @@ flake8-isort = "^3.0.0"
 pytest-cov = "^2.8.1"
 pytest-sugar = "^0.9.2"
 
+[tool.poetry.plugins."aleksis.app"]
+resint = "aleksis.apps.resint.apps:ResintConfig"
+
+[tool.black]
+line-length = 100
+exclude = "/migrations/"
+
 [build-system]
 requires = ["poetry>=0.12"]
 build-backend = "poetry.masonry.api"