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
IMO directive should always be present from the time page loads. This conditional logic is better applied *within* the directive itself (say inside the link function, the directive initializes picker when an "authorized" global event is triggered. )