py-flask-admin: updated to 1.5.3

v1.5.3:
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

(adam)