Clean, test and refactor the StorageManager component

[bgaillard]

Several updates have been applied to the StorageManager since the first release of the API.

The StorageManager source code is not clean, not well tested and documented, the following updates should be implemented :

• Remove deprecated methods
• Add shortcut methods to easier recurrent operations (get the access token, get the refresh token, get the date when the access token where retrieved, get the expiration time, get the expiration date, etc...)
• Move the code into a dedicated folder and create an abstract class AbstractStorageManager.
• The current StorageManager implementation should be an AbstractHtml5StorageManager and 2 other classes have to be created Html5LocalStorageStorageManager and Html5SessionStorageStorageManager