[FEAT] Level Info icons are now per-pack and per-style customisable

[WillLem]

SuperLemmix will now look in the level theme's style folder, and then the level's base pack folder, before settling on the default levelinfo_icons.png file.

This means that for custom sprites, these will always be displayed correctly in the Level Select and Talisman info screens (i.e. if the style author has created and provided a customised version of the file). Meanwhile, pack authors can customise these images for their pack even if it doesn't use a custom sprite set at any time.

However, the style path will always be preferred, so if a pack has a random lemminas level in the middle of it (for example), the version of levelinfo_icons.png provided in willlem_lemminas will display instead of the pack's version of the graphic.

NOTE: this only applies if the level's theme is set to willlem_lemminas - if the level simply uses a tile from willlem_lemminas, but has a different theme (i.e. one without a customised levelinfo_icons image), then the pack's graphic will be used instead. Or, if the pack doesn't have one, then the default will be used.

For styles, the alternative graphic goes into a new "levelinfo" folder (alongside lemmings, objects, terrain, grenades, etc.)

For level packs, simply place the alternative graphic into the root folder of your pack.

If you need any help with this, please ask. Editing this graphic can take a bit of time and effort, but it's worth it.

Implemented in Commit 36810d93a