The node_assign class holds the unique annotation combinations and the
assignment of the nodes to those combinations for use in visualization.
Slots
groupsthe unique groups, as a logical matrix
assignmentsnamed character vector providing association with groups
descriptionnamed character vector providing a description to group
colorsnamed character vector of hex colors for groups or experiments
color_typewhether doing group or experiment based colors
pie_locsif doing experiment colors, then pie graphs were generated here