Variant 1 (preferable for first cut)
arrow icon on the bottom of the manu hides the left side menu
providing only the possibility to restore it.
Later on, the v1 behavior can be enhanced - NOTE: this is not a subject for this ticket
when menu is toggled, only the root menu icons are displayed
click to the root menu icon goes to the default page specific for each root menu
There is some uncertainty currently how this may look&feel&work, the preference is
to postpone this work once the menu and its options are well known & defined.