Do not show input/output relationship edges when other regulation edges exist

[pkalita-lbl]

Currently the CX2 files we produce faithfully add edges for all types of relationships between activities. This means that we may end up showing "unnecessary" edges. For example, if there is already a "directly positively regulates" edge between two activities, then the "has input" relationship is somewhat implicit and doesn't necessarily need to be drawn -- even though that's what the GO-CAM technically says.

Here is an example on NDEx that shows this behavior:

The pathway visualization widget has some logic to collapse the "has input" (blue) edges, so it ends up looking like this:

The task here is to do a little rooting around in the pathway visualization widget codebase and see if we can reproduce its logic in the CX2 conversion code.