Additional metrics scroller fixes

• Make sure horizontal scroll arrows are visible on load
• Tooltip shouldn't be attached to metric's position before scroll
• Auto 'focus' on active/selected metric on load
• When you click on a metric that's not completely visible, slide so it is
• Allow variable heights so mockup can be accommodated
• Handle overflow for large currency balances and long labels

Testing

Test behavior of this thing at /wallet. At least one metric should be wholly/partially out of view for testing, so you might have to change your browser width until that happens (stop when one or more of those little left/right arrow buttons appears). For tooltip locations, see the same scrollable metrics bar at /analytics.

!686 (merged)