Include page loaders and parameterized pages in the default sidebar

[Fil]

(excerpted from #1624 / #1626)

[mbostock]

Not sure how we would include parameterized pages, unless we used the dynamicPaths option or link crawling #1627 to find the parameter values? But we definitely could include non-parameterized page loaders in the default sidebar; the main challenge there is that the default for the pages option is synchronous, but we could find a way around that by refactoring the code.