DAGRE graph support

FEATURES

• NetworkFrame now has a dagre option. If you set your networkType to dagre you can pass a dagre graph to the graph property of NetworkFrame and Semiotic will use some nice custom line and node rendering. dagre is not included in Semiotic (because of size) but you can import it into your project and get access to amazing DAG rendering like this:

https://emeeks.github.io/semiotic/#/semiotic/customnode

• NetworkFrame edgeType honors a curve type to draw those s-curves that D3 likes for dendrograms.

DOCS

• Added docs for dagre, ordinal snap brushing, some marginalia line labeling

FIXES

• Column names in OrdinalFrame were sometimes numbers and sometimes strings and it was causing issues that got fixed (thanks @agirton)
• OrdinalFrame tooltips no longer have the tooltip class because of collisions with other libraries that have CSS rules for that incredibly common class