Update flask-admin to 1.5.3

[pyup-bot]

This PR updates Flask-Admin from 1.5.2 to 1.5.3.

Changelog

1.5.3

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* Fixed XSS vulnerability
* Support nested categories in the navbar menu
* SQLAlchemy
 * sort on multiple columns with `column_default_sort`
 * sort on related models in `column_sortable_list`
 * fix: inline model forms can now also be used for models with multiple primary keys
 * support for using mapped `column_property`
* Upgrade Leaflet and Leaflet.draw plugins, used for geoalchemy integration
* Specify `minimum_input_length` for ajax widget
* Peewee: support composite keys
* MongoEngine: when searching/filtering the input is now regarded as case-insensitive by default
* FileAdmin
 * handle special characters in filename
 * fix a bug with listing directories on Windows
 * avoid raising an exception when unknown sort parameter is encountered
* WTForms 3 support

Links

• PyPI: https://pypi.org/project/flask-admin
• Changelog: https://pyup.io/changelogs/flask-admin/
• Repo: https://github.com/flask-admin/flask-admin/
• Docs: https://pythonhosted.org/Flask-Admin/