Adds config option to disable wraparound

[colinhanrahan]

While working on this, I overhauled agents' Von Neumann and Moore neighbors.

• Removed agent.vonNeumannNeighbors and agent.mooreNeighbors
• Removed update*Neighbors() functions
• Added agent.socialNeighbors because we still need asymmetrical adjacency neighborhoods for network overlay
• All other functions that used adjacent neighbors now use agent.cell.neighbors.values()
• cell.neighbors, previously a list, is now a dictionary with directions. If wraparound is turned off, cells on the edge will just not have directions that go out of bounds. For example, cells on the north edge will not have "northwest", "north", or "northeast" in their cell.neighbors dictionary.

Possible changes:

• Add another dictionary to distinguish between a cell's Moore and Von Neumann neighbors. cell.neighbors uses whichever neighborhood mode you picked in the config.

[colinhanrahan]

The new logic in updateNeighbors() looks just like cell.findNeighborAgents(). That function is only called in doLending(), which could just use cell.neighbors and add a check for agent != None like everything else. We can probably remove findNeighborAgents() (or if you really want, change the logic of everything else to use this function).