Display of mapped FCDAs shows incorrect mappings

[danyill]

In SEL devices ExtRefs are used to map an internal quality signal for a control block.

This shows up as null/null.null.

Suggest we don't show mappings for this case.

[danyill]

Specifically when we don't have:

• serviceType is not GOOSE or SV
• pServT is not GOOSE or SV

[danyill]

This also affects the hover tooltip when hovering of a line.