Make `hjem.extraModules` a single module instead of a list

[player131007]

Since we can merge deferredModules, hjem.extraModules doesn't need to be a list anymore. However, changing the type directly might be too big a breaking change. What do you think is the best course of action?

[eclairevoyant]

What's the benefit? To not have to type []?

[player131007]

What's the benefit? To not have to type []?

yes.

[eclairevoyant]

PRs with tests are welcome, as long as it doesn't break the existing type. We're not planning to prioritise this one though.