React Rally profiler feedback

[bvaughn]

Issue #1099

Demo build available at react-devtools-profiler-prerelease.now.sh

Flamegraph

• 49b9e47, 5cf07b2: Flamegraph/ranked charts should enable you to deselect the current fiber so the right hand pane shows commit statistics again. Perhaps this should be a new button in the top of the panel. Clicking in an "empty" space of the flame graph should also deselect.
• e03c7da: Show un-rounded durations on hover in tooltips for more info

Horizontal snapshot selector

• d5047c9, ea8e92c: Make the selected commit more prominent in the horizontal selector than just an alpha transform. Too many people didn't notice it. Maybe add an overlay pattern so it stands out more?
• ad38466: Left/right arrow keys should step through commits/snapshots.
• a2907c8: Make sure jumping from fiber-durations bar chart view to flame/ranked also horizontally scrolls the snapshot selector.
• 0c79424: When dragging, don't leave the dragging state until you release the mouse. (Even if you mouse outside of the selector.)

Right hand details pane

• 5cf07b2: Make the right hand details pane buttons blue so they stand out more as buttons.
• 6f075a5: Display "committed at" rather than "commit time".

Component durations bar chart

• 5e7de4e: It's not obvious which commits are visible in the component durations bar chart. Perhaps we could dim the commits thate are not visible in the above selector?

Elements tree view

• e881623: Single-click on the tree view toggle arrow doesn't expand/collapse the tree anymore. (You have to double-click it.)

General

• 27e1f29: "Show native nodes" probably isn't that useful– maybe add a settings/gear icon there and have a profiling preferences popup?
• 802932b, e8c4ecb: Add a preference (in the new profiler preferences popup) to filter commits below a certain duration too (to reduce noise in commit selector).

[bvaughn]

This doesn't resolve all of the requests in #1099, but I think it hits most of the low hanging fruit ones. I'll follow up on some of the others later.

If you don't have the time/energy to review this PR, I feel comfortable enough about it to just merge as-is. Just wanted to offer before plowing forward. 😄