Provide functionality to add and remove values, so that you can use a
sequential iterable as stack or queue if the underlying container
supports this. To this end, provide a way to specify whether the
value should be added or removed at the beginning or the end of the
iterable.
Change-Id: If63d302f3ca085e56d601116ce4dfaa6b94a0c4f
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>