Configurable timezone displays

Per https://github.com/urbanairship/tessera/issues/207, this adds a new option in config.py to control the display of times in graphite, nvd3, and flot charts. It makes use of moment-timezone, which required a version bump for moment.js. The change to get flot to show the correct time was also a bit of a mess

I also threw in a development dependency on [honcho](https://github.com/nickstenning/honcho) and added a Procfile to start `inv run` and `grunt watch` just a tad more easily.