Prosody now enforces some password policies, including a minimum length of 10
characters. If this fails, we currently show a rather unfriendly error to the
user. By adding this validation, the user should get nicer feedback and never
see that error.
There is a known issue that we don't currently validate all the policies that
Prosody does - for example, Prosody won't accept a password that contains the
username.
Ultimately we should fix the error handling anyway.
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 allows future App versions to also work with the invite page
without having to screen scrape the content.
Fixes#56 (at least for the portal side of things).
That seems to be some Quart-internal redirect which isn’t executed
correctly (probably due to our makeshift error handlers). So I
make this a proper redirect instead.
