`desc` query string arg incorrectly preserved when setting filters

[ibushong]

If you do descending order on a column, the URL will have ?desc=1. If you then apply a filter, this part of the url becomes desc=True, which breaks the ViewArgs parsing, resulting in the sorting going back to ascending.

One possible fix (I think..) is to remove the bool casting of the sort_desc argument to ViewArgs

[bekab95]

You May Make PR for this

[ibushong]

Steps to reproduce

1. Go to model list view (with data)
2. Sort by descending (e.g. click a column row twice) -- ensure that desc=1 is in the url
3. Apply a filter or search
4. Resulting url/view will have desc=True (instead of desc=1)

Cause

The jinja template renders sort_desc directly. Since it's a boolean, this becomes True in the html.

{# flask_admin/templates/bootstrap3/admin/model/layout.html #}
...
{% if sort_desc %}
    <input type="hidden" name="desc" value="{{ sort_desc }}">
{% endif %}
...

PR coming soon