Adding AngularJS directive

- Allows to be written as element or attribute
- Isolated scope with one property "viewId" which is only a string passed for the directive only
- Uses link function to apply "click" binding on the button which subsequently then handles all logic for using google client auth and picker api
- Scope uses $emit to send event to outside controllers to receive the data of the file chosen from the picker
@stulees better to inject and use $document instead