Include derived functions from imported modules

[nmacedo]

Functions without parameters defined in the main module show up in the visualizer. However, functions without parameters from imported modules are never included in the visualization (think of the next relation from util/ordering). This doesn't seem consistent since sigs/fields from imported modules appear in the visualization, and imported derived functions are still available in the evaluator.

[grayswandyr]

Very important indeed! I'll add this to the 6.1 milestone for this reason. Feel free to remove the milestone if that is too much work.

PS: IIRC, macros aren't imported either.

[nmacedo]

Here's how it would look for util/ordering. I left the names qualified to avoid confusion. Of course, these elements can be hidden/customized in the theme like any others.