Span meta: Compare with attached trace

[franzliedke]

Some spans can have a related trace (e.g. when a space refers to a HTTP request to a service that is also being traced with Mnemosyne).

When viewing the span meta information, it would be nice to also see the attached trace's meta information - in some cases (e.g. when an intermediate times out the request), this information can be different.

In the UI, this could be an optional feature (triggering the loading of the trace's information by clicking on a button):

This span refers to an external trace: [[VIEW TRACE META]]