moving Silva Image to a extension
We might want to consider moving Silva Image (with all of its manipulation
functionality etc.) into a seperate Silva Extension, and keep a very lightweight
image asset in the core. That way we can safely depend on PIL for this
extension, where the core's dependencies are kept to a minimum.
(A cool idea, that's actually Martijn's :)
This might also relate to the existing ideas on refactoring the assets in Silva.