toolbar: move the new folder/tab/bookmark items into the shared popover

The files view creates and owns these buttons currently, meaning they
aren't shown on the menu when the Other Locations view is active.

This change moves the menu items from the view's toolbar menu ui file
and into the ui file for the shared popover, so that the buttons are
also shown for Other Locations.

https://bugzilla.gnome.org/show_bug.cgi?id=764632