Refactored AppDelegate for hybrid apps to make the post install script unnecessary for the cordova plugin

Also updated the cordova plugin repo (got rid of the post install script, updated plugin.xml and update.sh), see:

https://github.com/wmathurin/SalesforceMobileSDK-CordovaPlugin/commit/3f4f19b9e45eacf450f4e3e3622d0ae236822db9

and

https://github.com/wmathurin/SalesforceMobileSDK-CordovaPlugin/commit/63ffb2cb8db076a3a87af1b798a31b24808e6673