Added .clickable class to CSS.
Added the 'References' metadata property to graph nodes, so we can display references to other nodes.
Switched back to .classed(), since it actually does do what .attr() does here, only simpler.
Reworked digraph directive to add labels next to nodes for various things.

Also, cleaned up existing code a bit and made some of the behavior a bit better.
Discover data types at connection time, and map data type IDs to names in 'fields' events.
Added tooltips to column headers, showing what data type each column contains.
Fixed border radii on headers in tables with only one column.
Remove margin from pre:only-child in _all_ tables, not just popups.