Added sub-centralities

Added sub-centralities to the centrality control to control inter- and
intra-cluster connections.
Simplified Centrality Subtypes

Simplied the sub-centralities introduced in last commit into a boolean
for inter vs. intra- cluster.
Also implemented centrality color inversion.
Centrality Caching

Implemented a caching system for degree and closeness centrality to
improve performance. Also added timer to right click menu. Considering
removing it and adding functionality to selection menu.