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).
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
Instead of processing the input further and forwarding the
credentials to prosody, we catch the error early on to prevent
having to handle the 400 error code specially and to prevent the
password from spilling in other components.
Fixes#55.
- Avoid fighting import cycles using a factory function
- Collapse useless subpackages into simple modules
- Move flask plugins / infrastructure in own module
- Refactor how blueprints are used to localize information about
URL routing to app factory
