Some more SpecialPageHtmlFragment sublasses
This patch turns all classes that require an ImportPlan as the only
parameter into subclasses of the previously introduced
The getImportDetailsHash() method introduced in this patch is a little
awkward. It is currently used 3 times in code that appears duplicated.
There are probably better ways to refactor these. However, I would love
to go step by step and explore this further in later patches.