fix tabs: add timeout on tab links

Before, when clicking on a tab link, the tab was changed before any
click handlers had time to receive the click. By adding a timeout, the
click is managed by all the handlers that have to manage it before the
tab is changed. For example, the dropdown close as expected when
changing a tab.
fix dropdown: increment z-index for use in dialog

Dialog and dropdown had the same z-index, resulting in the dropdown
appearing below the dialog. By incrementing the z-index of the dropdown,
it's fixed.