[FastAPI] add /tu/ (get) index

Primary commit of this MR:

add /tu/ (get) index

This commit implements the '/tu' Trusted User index page.

In addition to this functionality, this commit introduces
the following jinja2 filters:

- dt: util.timestamp_to_datetime
- as_timezone: util.as_timezone
- dedupe_qs: util.dedupe_qs
- urlencode: urllib.parse.quote_plus

There's also a new decorator that can be used to enforce
permissions: `account_type_required`. If a user does not
meet account type requirements, they are redirected to '/'.

```
@auth_required(True)
@account_type_required({"Trusted User"})
async def some_route(request: fastapi.Request):
    return Response("You are a Trusted User!")
```

Routes added:

- `GET /tu`: aurweb.routers.trusted_user.trusted_user

Signed-off-by: Kevin Morris <kevr@0cost.org>