The index color filter currently only generates a custom palette. This patch adds the ability to have it use a kocolorset or a koabstractgradient as a palette source, potentially reducing time on the user's part configuring things.

It seems to work here, but my brain is shutting down on the possible errors. I mostly am storing it here till my brain works again.

Also, it adjusts a filter config file, so it might be an idea to wait with merging it until the animation config stuff is merged.