FramePacker sort only *remaining* frames to pack, because when we skip the index forward by the number of frames we packed, we won't necessarily be skipping the correct frames (since we skip in the *UN*sorted array). Instead, sort this.frames at the start of FramePacker process

Exporter.fla now grabs sprite-style frames and packs them to sheets (no return data yet)

FramePacker has an outline of an algorithm to get good sheets out of a list of rectangles (next: get those rectangles!)

Start a packer that works purely on rectangular bitmap areas (export type agnostic). How should we determine best sheet size?