Companion PR to https://github.com/koreader/koreader/pull/9586 (#1525)
Companion PR to https://github.com/koreader/koreader/pull/9586 (#1525)

* Minor cosmetic tweaks to ffi/pic to follow our usual class semantics
NiLuJe/koreader-base,koreader/koreader-base,koreader/koreader-base,NiLuJe/koreader-base,koreader/koreader-base,NiLuJe/koreader-base,koreader/koreader-base,NiLuJe/koreader-base