Optionally mask all local/intermediate spans

[codefromthecrypt]

When doing network investigation, local (not remote) spans can interfere with intuition. For example, local spans make trace depth less useful, span count less useful. It also makes the trace bigger and harder to view. Adam from Atlassian suggested that the UI could disable local spans in the trace view, possibly with a checkbox or something. This would help them remove clutter when trying to figure out a problem.

cc @openzipkin/ui

[beckje01]

I like it as optional, I still times I want to see local spans