Fix off canvas menu and icon buttons for mobile devices
The icon bar breaks into a second row, if the screen size goes below 400px width. I've made an acceptable fix for the current situation and should be adopted to the Publisher app -> http://admin.exist-db.org:9090/HistoryAtState/guides/commit/d8ad91a3841f5e06180a1be2dd8ab6c0990ea298
In order to provide Tei-Publisher app users being able to add a flexible number of icons, the layout has to be styled with "flexbox" display rules instead of Bootstrap floating classes.
The effect is, that elements will expand evenly within the given space. Also, the ordering of elements can be controlled and swapped easily, if necessary.
Btw: Flexbox should be also applied for the panel boxes as well to get rid of Bootstrap's pull classes and reverse markup ordering.
Off Canvas Menu
Should be available also on mobile devices and has to be fixed, not just be hidden! Otherwise, the navigation of subpages is not possible.