Make it hidden, by default. Unify style with other items in the navbar
(making version list horizontal, for example). Show current version next
to the caret mark that opens the menu.
(cherry picked from commit e036d26953)
Make the list of available versions dynamic. The items displayed is now
generated with javascript. The parent directory of the site is supposed
to contain versions.js providing getVersionListItems() that returns the
available versions.
The update-gh-pages.sh script is modified to update/create versions.js
on every invocation. It simply lists all directories in the root
directory and adds them to the version list.
(cherry picked from commit c05c6f2e5b)
