In-trace search should allow navigation between results

[yurishkuro]

Currently if we use the Search box on the trace view, it grays out all spans not matching the search and keeps the matching span in normal opacity. However, on a large trace this makes it difficult to find the matching spans.

Suggestion:

• scroll the trace view to the first matching span automatically if it's not currently in the view port
• add the navigation buttons to the Search bar that allow jumping forwards/backwards between the matching span, similar to how in-page search works in Chrome - it shows up and down arrows, and by default the Enter key jumps to the next match.

[tiffon]

Great suggestion.

FYI, something tangentially related, in #93 I've added shortcuts to scroll to prev / next visible span. When a search is in-progress, this skips spans that are filtered out.