GRAPH 1: Layout improvements

[arniebradfo]

This is part 1 of a series of stacked PRs meant to isolate issues if they arise. #117

Description

Improve the graph layout so nodes are more spaced apart and less likely to overlap

• improve the d3.force() compatible forceClampToRadius by making the forces softer. This was the primary cause of the overlap issue.
• tweak other forces spacing
• tweak the radius calculations so they cascade on each other
• split HierarchicalGraphRenderer extended classes' constructors into more defined methods: initializeForces and initializeSelection
• There are also now methods to toggle force direction: GraphHandler.useGraphForces() and GraphHandler.useSimpleForces(). The simple forces only include collision detection so a user can create a very precise layout.
  • These have not been implemented in the UI, but could be in the future. Maybe in a 'Graph Settings' panel.

Testing

• look at several different graph layouts. Does anything overlap?
• does the typical graph interaction still work?
• hiding and showing content

Screenshots

No screenshots since the graph 'looks' the same. It just has less error edge cases and is more fluid in interaction.

[ccarpenter28]

When an item (beacon, host, etc.) is hidden/shown, the graph jumps around on the screen and does not stay centered. I checked the develop branch and also noticed it happening there, although it is more severe in that branch -- the graph moves completely off-screen in develop. Since the behavior isn't quite the same, not sure if you want to handle the graph movement in this branch or separately.