Navbar slide animation once in a while gets the wrong heigh

[rundis]

To support the slide up/down effect I ended up wrapping the collabsible part in another div. Then I'm using debois/elm-dom on the collapse menu button click event to get the height of the hidden collapsed menu(-bar). Works most of the times, but sometimes it's getting the height of the element after the navbar which produces really funny animation results.

(also see #5)

[rundis]

I think I managed to fix this one. The reason was that when clicking on the edge of the hamburger menu (navbar toggler), the target became the nav root item rather than the button. That messed up the logic for locating the element we need the height for to support the animation.