new: support search placeholder

Merge branch 'feature_multiple_default_sort' of https://github.com/stepsame/flask-admin into sqla-sort-multiple

Merge branch 'case-insensitive-filter' of https://github.com/jnga/flask-admin into case-insensitive-mongo

Fix #1715 python3 exception has no attribute 'message'

Add missing class_name to bootstrap 2/3 menu items

This is part of the code, but wasn't in the template.

https://github.com/flask-admin/flask-admin/blob/v1.5.2/flask_admin/menu.py#L133

Error in Ukrainian translate 

Change Ukrainian translate error

Upgrade leaflet