Google Drive action and refactorings to Slack and Rackspace Cloud Files actions.

Google Drive action
* Uploads files to Google Drive.
* It displays a dialog for each upload to select the desired folder or create a new one.
* It remembers selection, so for each upload it will preselect the previously selected/created folder.
* Handles authentication and stores the neccessary data in a file in the action folder (used the sample provided by google for their api)

Refactored a bit the code from Rackspace Cloud Files and Slack actions so it resembles more Ruby than Java :)