Make sure they all have the minimum height based on what is currently
the hardcoded value of the button.
Also inlclude the border top and bottom padding in the layout in case the
font is really big
The Flickable should already have sane default
But we need to make sure that the default binding don't override bindings
set with aliases. So we must use BindingsMap::set_binding_if_not_set which
sets the priority properly
Closes#581
