PSK 3.0 - Written for Polymer 2.0!

Convert psk to use polymer 2.0 (#967)

* Convert psk to use polymer 2.0

* update tests for 2.0

* load webcomponents.js polyfill without js check

* add handling for undefined observer values

* update to latest polymer config property names

* fix eslintrc spacing

* use the google eslint ruleset

* bind the callback we send to importHref

* add comments to test/index.html

* reference polymer-element.html instead of polymer

* add slot=header attribute to app-header

* fix js line length

* add webcomponents-loader

* Update polymer.json

* respond to feedback

* convert config to properties & observers methods

* Hide drawer-toggle

* Update webcomponentsjs version to webcomponents/webcomponentsjs#^1.0.0-rc.1