Fix various bugs introduced with heading

Summary:
This fixes:
- Indented notifications line (it's back)
- Heading being non-clickable
- Buttons not being right-aligned in history
- Keyboard navigation
- Long app names

Reviewers: #plasma, broulik

Reviewed By: #plasma, broulik

Subscribers: ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D29234