Allow user to specify that generated ZIM should use `nopic`

[hamoudak]

can I make nopic zimfile with wp1 ? If it doesn't. could this be done?

[kelson42]

@hamoudak For now it is not possible AFAIK

[audiodude]

Correct, we don't currently have that capability, but it should be easy enough to add. I've updated this issue title to reflect that, we'll use it to track. Thanks for the suggestion!