NodesController index performance enhancement

* By using eager_load instead of includes, AR is forced to use
  joins as much as possible, cutting down on # of queries.
* Poi has a scope method to do the eager_load chains.

Additionally, I added a few things to .gitignore and deconfigured
librato to cut down on librato-rails warning messages.
reverting .gitignore and librato.yml changes
Merge pull request #1 from halfbyte/nodes_controller_perf

NodesController index performance enhancement