Allow images as campaign intro/outro in place of videos (or support better video formats).

[Spatulade]

(Just putting this here as this was discussed earlier today)

Campaigns currently support .smk files for the intro and outro, but these files are very difficult to make. One thing that may work as a compromise could be to support static images as well.

Hopefully it is possible to either bypass this or use the code for the splash screens. Currently splash screens use their own separate palettes, but it is probably enough to allow the standard ingame palette for these images.

Alternatively, maybe it will be possible to use a newer, easily and freely available video file format (assuming there is an easy way to ensure such a video file has the right settings and restrictions to work inside the game, as it presumably has a limit to the number of simultaneous colours per frame).