Improved styles for argus tree view.

Addresses #44. Improvements include:
 - more distinct dashed (taxo) vs. solid (phylo) edges
 - third style for edges with taxo+phylo support
 - more conventional black-and-white scheme
Reserve true black for phylo-supported edges.

Also conflate path styles for all edges with phylogenetic support,
whether or not they are also supported by taxonomy. Addresses #44.
Merge pull request #471 from OpenTreeOfLife/new-argus-styles

Improved styles for argus tree view