martijnb92

[4.1] Make header classes configurable

1

While adding some `offset` classes to the content I noticed the header was no longer aligned. This PR adds the ability to define classes for the CRUD headers, usefull when...

# Feature Request ### What's the feature you think Backpack should have? At the moment Backpack still uses a select2 theme which is for Bootstrap 3, (https://select2.github.io/select2-bootstrap-theme/ / https://github.com/select2/select2-bootstrap-theme) this...