Looser linkstrength on clustering
Team dataset filled out for better cluster testing

Both "cluster" and "node_type" can be used for clustering now. They are
roughly, but not exactly analogous, making it easy to see if clustering
is working as well as whether clustering by different keys is working.
Do not recreate quadtree function everytime

D3 quadtree works by generating a function that can be called on each
tick.  We were creating a new quadtree every tick.  Instead I've moved
it up to the layout constructor so a new one is made only when we make a
significant enough change to the layout to make a new one.
D3 internals passed to quad tree generator
Remove edge css for alchemy-white
Merge pull request #422 from MDCox/clustering

Clustering