This will trigger a rate limitation when the username does not exists or
if the password is not the correct one. The time to wait is exponential
(base 2) after the 5 first attempts.

This is done by splitting the original function in an inner function
that manage the creation of the image in a PIL format. This inner
function is decorated with the redis cache function.

Because of a bug in the PIL library, we can not unPickle a tiff image.
The workaround is to use the following code:

    if isinstance( img, TiffImageFile ):
        if not hasattr( img, "use_load_libtiff" ):
            img.use_load_libtiff = True

Source: https://github.com/python-pillow/Pillow/pull/4565/files

This being patched in the current versions of PIL, we should be use this
monkey-patch for new version of Python.

Since the variable is global anyway, we don't need to pass it as
parameter.

The fetch of the data don't need to be done in an ajax query once the
page is loaded. This will directly populate the "secret" javascript
variable and the 'input' field.

The remaining time and the current TOTP are not useful in the current
workflow.

This is the same order as for the other pages (help on the left, next on
the right).

This will only use one div to the errors and OK messages. The
notification for the use is done via a function call instead of editing
the corresponding divs.

This will not display a message to the user if the TOTP is correctly
set, but will redirect him to the next step automatically.

The user is now obligated to provide the TOTP value to continue. If not
provided, the user can still re-open the current page to get help or
retry the configuration process. This should remove the miss configured
account by not reading the configuration dialog (the user has to provide
at least once the TOTP to be able to finish the configuration; if the
TOTP value is set in the database, the configuration has been done at
least once).

The buttons should now be the correct size in regards of the outer div,
even when the page is resized.

Before, for some page size, when there was just not enough space for one
button more, the outer div was shrunk, but the button was not, hence
producing an overflow of the button, which was not nice to see.

If not present, the default is assumed to be "touching" and "none"