Planner: actually return the error

Just setting it up is only half of the solution...

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Profile: Don't disconnect too many signals

If we disconnect the picture releated signals then in dive add and dive
plan mode the pictures from the last shown dive could appear on the
profile. That's not cool.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>