GraphicsMagick can’t process animated GIFs well unless all frames are coalesced, which creates very large files.
This means there is a new dependency on Gifsicle which is very good at working with animated GIFs.
- Thumbnails are still processed through GraphicsMagick (more options, e.g. centre-crop)
- Large previews of animated GIFs go through Gifsicle
The startup checks are updated to check for the Gifsicle binary.
Fixes#96.