Previously, any messages only intended for the user (status messages,
warnings, errors) were sent over stdout. The actual emoji items are also
sent to the pickers over stdout so they would sometimes pick up the
messages and show them as an option to pick. If history is enabled, we
then also save the falsely included items there to forever display as an
option.
This commit changes internal messages to all be sent over stderr
instead, so they should not be picked up by any external programs we
hand off to.
