Turn off nginx buffering to allow for streaming APIs.
Mongo 1.3.20 has disappeared from npm. Revert to 1.3.19.
Remove unused mocha.opts file (the settings in Gruntfile.js are used).
Resolve mongodb connection drop issues (I think).

By switching the mongo connections from the raw Mongo adapter to
Mongoose, this seems to fix NREL/api-umbrella#17.

Mongoose uses the same underlying mongo driver, so why this fixes it is
a bit confusing. My only theories are:

- It's related to how Mongoose connects and the keepalive setting.
  Mongoose doesn't use the newer MongoClient.connect approach, and on a
  quick glance, there are maybe some differences in how keepalive
  settings get passed with the new MongoClient.connect).
- Or it's Mongoose's query buffering that helps resolve this issue.
  While we don't need most of Mongoose's extra features, its ability to
  buffer queries when in a disconnected state might be what fixes this.

Assuming this ends up working, the retry logic in api_key_validator.js
should be revisited.
Merge branch 'master' into gsa