[Mobile] Restore adaptive layout for small screens
Unfortunately, the responsive layout defined within media breakpoints has been dropped since refactoring to 4.0.0-RC1. Some of the adaptive css rules are missing now and have to be restored.
- The navigation bar should collapse and provide a dropdown menu for its items and.
- The logo should scale down accordingly to the given navigation bar height.
- The toolbar should get a different concept, as many new features have been introduced now. Maybe only icons should be displayed, or an off-canvas drawer on the right will be helpful. Most of the time, it won't be used anyway and could be moved off the screen to make space for more content.
- The font-size should scale up/down according to the screen dimensions within a minimum and a maximum size.
- The navigation bar and the toolbar should have a smaller height on small screens.
- Horizontally stacked grid elements should be stacked vertically on small screens to avoid horizontal scrolling wherever possible.