Get rid of `buttons-panel` class name

[glebfox]

It now can be replaced with hbox attributes (the last one is wrap)

[glebfox]

For QA:

• Check that all system views still position pagination at the end of buttons panel
• Check that all view templates uses width=100% and wrap=true instead of class names
• Check that on narrow screens buttons panel content wraps to a new line

P.S. Worth checking at the same time with #4865