History object

[miratepuffin]

We intend to move all of the history based functions onto a singular 'History' object which we can then extend with several helper functions for the typical analysis users are doing on the history.

This means the basic stuff will become:

node.history.additions 
node.history.earliest time 

and we can start to add functions such as:

node.history.stability(period) #return some metric about how often the node leaves and rejoins the graph
edge.history.increments.mean #What are the average increments between updates