Revert "Upgrade to quart 0.15"

This reverts commit 486596f89f.
It was discovered that multipart/form-data forms do not work
correctly with Quart 0.15. The upgrade to Quart 0.15 was rushed
and not tested correctly, which I apologize for.

See-Also: https://github.com/pgjones/quart/issues/126

snikket_web/user.py

@@ -1,7 +1,6 @@
 import asyncio
 import typing
 
-import quart
 import quart.flask_patch
 from quart import (
     Blueprint,
@@ -12,7 +11,7 @@ from quart import (
     flash,
     current_app,
 )
-import werkzeug.exceptions
+import quart.exceptions
 
 import wtforms
 
@@ -93,8 +92,8 @@ async def change_pw() -> typing.Union[str, quart.Response]:
                 form.current_password.data,
                 form.new_password.data,
             )
-        except (werkzeug.exceptions.Unauthorized,
-                werkzeug.exceptions.Forbidden):
+        except (quart.exceptions.Unauthorized,
+                quart.exceptions.Forbidden):
             # server refused current password, set an appropriate error
             form.current_password.errors.append(
                 _("Incorrect password."),