Introduce ActionToolbar

Summary:
A toolbar which represents a list of actions with a series of ToolButtons.
When there is not enough space for all the toolbuttons, put some of them under a menu triggered by a "..." overflow button

port Card and InlineMessage private implementations to this

Test Plan: Card and InlineMessage have the same behavior

Reviewers: Kirigami, hein

Reviewed By: hein

Subscribers: apol, davidedmundson, plasma-devel

Tags: Kirigami

Differential Revision: https://phabricator.kde.org/D13433