BUG: 385973
Use a consistent ToolBar for every page's header, with the same background color, height, and text size. This yields the following benefits:
- Eliminate user complaints about image banner headers
- Add an area to place UI controls, such as the much-requested sort order menu button (https://bugs.kde.org/show_bug.cgi?id=383518)
- Increase internal UI consistency; now everything uses the same header style except for the main Featured page (which I think deserves a banner, just with a better image)
- Widescreen mode looks better because each view doesn't have its own header style
Also remove the redundant app name from the App page's header, and make the back button a standard button to visually balance the header
TBD: implement the same style for the search page