Pipelines: Add page listing modules

[ewels]

Each module says which pipelines use it, but we don't have the inverse.

It'd be nice to have the inverse: a tab on the pipeline pages listing all modules that are used. Can be summary boxes, similar to the main modules listing page.

[mashehu]

we are running out of space for tabs on <20" screens imo. how about adding it to the sidebar similar to how it is on the modules pages