Improve source code lookup feature

[bhufmann]

For later, let's handle hyperlinks?

I think in the Properties view, if the key is "Source" the TraceExplorerTooltipWidget assumes that the value is a source code location. It tries to match filename and line number and adds a handler to open the file. The assumption is not always correct, because the Source column could be, for example, source IP address or similar things. So, this source code lookup feature will need to be addressed differently (more standardize), which is outside the scope of this PR. I'll open a new PR for to track this.

Originally posted by @bhufmann in #357 (comment)