This PR improves navigation bar with several changes such as:
moving Kachna Online logo to the centre again (the logo have been shifted slightly to the left by the loading spinner taking a place in the row as an invisible item),
showing only dropdowns in hamburger menu for mobile devices instead of small split-dropdown buttons,
add buttons to dropdown collapse for missing clickable main part of split-dropdown buttons when the split-dropdown buttons are replaced by the normal dropdown buttons for mobile devices and
This PR improves navigation bar with several changes such as: