Simplify build process

**Use webpack to build the exported library.**

* The build is now a UMD bundle so it will work as a global, with AMD, or CommonJS.
* No real changes required to get this working with CommonJS modules (see the POC branch).

**Karma housekeeping**

* Install karma-cli for convenience of npm-scripts.
* Remove phantomJS launcher.
need to remove this before merge.