Add support for changing editor encoding

* Upgrades pathwatcher and text-buffer for new encoding APIs
* Adds a new [encoding-selector](https://github.com/atom/encoding-selector) package that mirrors the grammar selector behavior
* Put the current encoding on the status bar
* Allow changing of the encoding
* Add auto detect option that uses [jschardet](https://github.com/aadsm/jschardet)

![encodings](https://cloud.githubusercontent.com/assets/671378/4818732/4680b1c8-5ef7-11e4-9ce2-8f68e58fb9a7.gif)


Closes #1806