This change includes the following updates:
* Script tags are moved out of dom-module element
* <template strip-whitespaces> is changed to <template>
* gr-js-api-interface.html is splitted to avoid <script...> after
<dom-module>
* gr-app initialization moved to a separate file. Without this change
polymer-modulizer places initialization code after other imports
* gr-external-style - move importHref in a separate _importHref method.
It is not possible to mock Polymer.importHref method in tests after
conversion to ES6 modules.
Change-Id: I97bae910c5d0df1bf8e6778657173729f0a6652a