Bump quart to version 0.17

This is needed because jinja2 had an update which caused the portal to
not work at all:

```
ImportError: cannot import name 'escape' from 'jinja2'
```

Quart needed updating for that.

This update required a lot of typefixes. Apparently, the "canned"
responses (like redirect) are now plain werkzeug responses, while
quart.Response does not inherit from werkzeug.Response (otherwise, we
could've changed the type annotations to werkzeug.Response everywhere,
but that doesn't work because a quart.Response is not a
werkzeug.Response).

P.S.: This time, I *did* check that avatar uploads don't break (see
b007afc).

snikket_web/user.py

@@ -13,7 +13,7 @@ from quart import (
     flash,
     current_app,
 )
-import quart.exceptions
+import werkzeug.exceptions
 
 import wtforms
 
@@ -96,7 +96,7 @@ async def index() -> str:
 
 @bp.route('/passwd', methods=["GET", "POST"])
 @client.require_session()
-async def change_pw() -> typing.Union[str, quart.Response]:
+async def change_pw() -> typing.Union[str, werkzeug.Response]:
     form = ChangePasswordForm()
     if form.validate_on_submit():
         try:
@@ -104,8 +104,8 @@ async def change_pw() -> typing.Union[str, quart.Response]:
                 form.current_password.data,
                 form.new_password.data,
             )
-        except (quart.exceptions.Unauthorized,
-                quart.exceptions.Forbidden):
+        except (werkzeug.exceptions.Unauthorized,
+                werkzeug.exceptions.Forbidden):
             # server refused current password, set an appropriate error
             form.current_password.errors.append(
                 _("Incorrect password."),
@@ -128,7 +128,7 @@ EAVATARTOOBIG = _l(
 
 @bp.route("/profile", methods=["GET", "POST"])
 @client.require_session()
-async def profile() -> typing.Union[str, quart.Response]:
+async def profile() -> typing.Union[str, werkzeug.Response]:
     max_avatar_size = current_app.config["MAX_AVATAR_SIZE"]
 
     form = ProfileForm()
@@ -221,7 +221,7 @@ async def manage_data() -> typing.Union[str, quart.Response]:
 
 @bp.route("/logout", methods=["GET", "POST"])
 @client.require_session()
-async def logout() -> typing.Union[quart.Response, str]:
+async def logout() -> typing.Union[werkzeug.Response, str]:
     form = LogoutForm()
     if form.validate_on_submit():
         await client.logout()