✨ Add Items (crud, models, endpoints), utils, refactor (#14)

* Update CRUD utils to use types better.
* Simplify Pydantic model names, from `UserInCreate` to `UserCreate`, etc.
* Upgrade packages.
* Add new generic "Items" models, crud utils, endpoints, and tests. To facilitate re-using them to create new functionality. As they are simple and generic (not like Users), it's easier to copy-paste and adapt them to each use case.
* Update endpoints/*path operations* to simplify code and use new utilities, prefix and tags in `include_router`.
* Update testing utils.
* Update linting rules, relax vulture to reduce false positives.
* Update migrations to include new Items.
* Update project README.md with tips about how to start with backend.

{{cookiecutter.project_slug}}/backend/app/app/models/item.py

@@ -0,0 +1,34 @@
+from pydantic import BaseModel
+
+
+# Shared properties
+class ItemBase(BaseModel):
+    title: str = None
+    description: str = None
+
+
+# Properties to receive on item creation
+class ItemCreate(ItemBase):
+    title: str
+
+
+# Properties to receive on item update
+class ItemUpdate(ItemBase):
+    pass
+
+
+# Properties shared by models stored in DB
+class ItemInDBBase(ItemBase):
+    id: int
+    title: str
+    owner_id: int
+
+
+# Properties to return to client
+class Item(ItemInDBBase):
+    pass
+
+
+# Properties properties stored in DB
+class ItemInDB(ItemInDBBase):
+    pass