Show a short message below the existing chat mentions message that is shown in the top left area of the editor above the layers/images/sounds button when the player character is moved ingame while the editor is open. The messages are cleared when the editor is activated and when the client is disconnected.
Closes#1993.
The `Append` method was returning `0` on success while `Load` and `Save` were returning `1`.
Now all three methods use a `bool` as return value and return `true` on success.
The call `SortImages()` is moved inside the `Append` method, as it should always be called when appending succeeded.
Purely automatic change. In case of conflict with this change, apply the
other change and rerun the formatting to restore it:
$ python scripts/fix_style.py