Make include-what-you-use happy with some files in source/ps and fix
what needs to be fixed.
Delete source/ps/FutureForward.h as it is no longer used.
Ref: #8086
Signed-off-by: Ralph Sennhauser <ralph.sennhauser@gmail.com>
Only the sender and the recipients receive the chat messages.
This commit only has an affecto on messages where the addressee(s) are
selected through the dropdown. Addressee(s) selected with a "/" command
are still sent to evevyone and filteret by the receiver.