DIRECTOR: Add support for film loops

[moralrecordings]

The last big primitive in Director that we don't support: film loops! Typically you create these by doing an animation spanning multiple frames and channels, then selecting the whole lot and dragging it to the Cast pane. This creates a new Film Loop cast member which is essentially the whole sequence flattened down. Showing the same Film Loop cast member over multiple frames in the same channel will increment the animation.

Eastern Mind has a number of places which use film loops (e.g. the snake in the intro dialogue), without this several animations will be missing.

Lots of scripts in Total Distortion rely on film loops existing in the cast, so without this can sometimes lead to softlocks (battling the guitar warrior) or buffer underflows (looking at the fish tank on the top floor).