Additional picker service and directive refactored to use services

- Modified svc-gapi.js to add a "pickerLoader" service for loading the google picker api
- Added svc-picker.js to provide a service for getting the google picker api (essentially window.google)
- All services now pertain to the "rise vision.widget.common.google-drive-picker" module to encapsulate these services for just the google drive picker
- Removed unnecessary config value from all config files (dev,test,prod) as this is used an Angular value now
- Directive completely refactored to make use of all services available now
- Removed google-authorization.js, not needed anymore
- Updated "angular" gulp task to include the service files in concatenation
- gapi-mock.js modified to now use handleClientJSLoad and also fixed window.gapi.load function for executing the callback
- e2e test HTML updated to now load gapi-mock.js (or real google api) last, after the directive to ensure handleClientJSLoad exists which resides in svc-gapi.js
IMO Wrapping logic into a "get" function isn't necessary. Because the name of the service, ```pickerLoader``` has correctly confined its functionality into a single purpose: to load the Google Drive Picker library.
With that said, the provider itself could just be the loader function, instead an object that contains a get() function.

I have been debating whether I should get rid of get() in a few other places: gapiLoader, oauthLoader, etc. I'm leaning towards the change right now, but am open to discussions. 

@stevesherrie @tejohnso @alex-deaconu @olegrise FYI.