Header bar redesign

New scalable header bar design which should scale nicely with height and width changes by collapsing several elements (putting them into popups and overflow menus). The height scaling is similar to Elisa.

This was the original situation:

Edit: updated screenshots (volume controls are now always at the end of the toolbar and in popup)

These are screenshots of the new UI header bar controls:

Default wide window:

Narrower (removing text from toolbar buttons):

Narrow (all buttons into overflow menu):

Most narrow (remove timestamps next to slider):

Scaling the header height to smaller dimensions (scaling image and removing text):

Header heigth fully collapsed (background color back to Theme; small episode image at the left of toolbar; looks a bit like the status quo):