Add "exclude" feature to visualization

[hftf]

To reduce clutter and noise, I would love the ability to blackbox (either exclude or collapse into a single node) commits matching some criteria:

• all commits before a certain date or commit, or
• all unexplored commits (e.g. highlighted in blue below)

See also #40 (but that may not exhaustively solve this issue).

Inspired somewhat by the blackboxing feature in Chrome Dev Tools.

[aspiers]

Thanks very much for the feedback :-) Actually, it's already possible to exclude all commits before a certain commit via:

git deps -s -e COMMITISH

This is specifically useful in the backporting use case as demonstrated in this video.

However I acknowledge this is not a very flexible approach, and it would be better if stuff could be trimmed dynamically from the UI after it has already been displayed. #32 was one suggestion of how to do that by manually collapsing expanded dependencies, but exclusion based on ancestry or dates would also be useful for sure.