ISDR: Add Contributor Keys

[Rajia]

Per Fred's request, Account button should provide you with the option to use a contributor key.

[Rajia]

Contributor Keys are now implemented in the API and a respective uploadDataSet call is available that takes a contributor key and name (name is arbitrary, use "iOS App") instead.

They are not currently added to the credential manager dialog because they are not in the Android's credential manager dialog yet either. So what needs to be done, is their needs to be a dialog for entering a contributor key if the user hits upload and is not logged in (using UIAlertView with a single text field for the key).