Experiment with subscriber counts

In addition to adding this as a node attribute, would likely be a better metric for sizing nodes and identifying prototypes for labeling communities. Take for example the PS4 cluster:

* /r/PS4: 374k subscribers, 3052 active
* /r/DestinyTheGame: 300k subscribers, 7671 active
* /r/xboxone: 296k, 2998 active
* /r/RocketleagueExchange: 27k subscribers, 8587 active

Preferably, this would have been identified as the PS4/XboxOne cluster. /r/xboxone is just barely smaller than DTG by subscribers, so what're ya gonna do, but RLE is way smaller by subscribers than either PS4 or XBO. Exchange subreddits tend to be extremely active due to the high velocity of posts and incentive for user interaction, so the 'active users' labeling method failed on this cluster.

Of course, there's nothing preventing me from re-labeling clusters by hand after the fact if I deem necessary. Active users seems to do a pretty good job most places. Still, I suspect going by subscriber count will work better for this.