Blender Git Loki

UI: Use better icon for identifying assets

Use the `ASSET_MANAGER` icon which is more appropriate than the current one
which was just an unused icon that seemed sorta fitting, but was only meant to
be temporary.
The `ASSET_MANAGER` icon is already used for the Asset Browser, so it's being
reused which we normally avoid. So we may still want to create a dedicated one,
maybe a variation of this one.