Displaying certain node levels from center node

[angcast]

A user can select a node to be the center node [either through search, click, etc...], and how many levels they want to see. We can filter out the graph to display this. This will be helpful when a user wants specific data in a large amount of data.

• Implement react selector
• Implement 1st degree
• Implement 1.5 and 2nd degree
• display 2nd degree nodes less prominently than 1st degree nodes (see http://www.sixdegreesoffrancisbacon.com/?ids=10000473&min_confidence=60&type=network)

[srisi]

Idea for this feature comes from the "visual density" selector from http://www.sixdegreesoffrancisbacon.com/?ids=10000473&min_confidence=60&type=network
For our purposes, we'll focus on :
1st degree (direct connections of the main node to other nodes)
1.5 degree (1st degree + connections between nodes connected to the main node)
2nd degree (all connections from/to nodes connected to the main node)