Bug 1032629 - APN Settings UX refresh

https://bugzilla.mozilla.org/show_bug.cgi?id=1032629
The APNs added through client provisioning messages are enabled with an additional property which is an unique identifier (```_id```). As the carrier might send the same APN several times we add this extra property in the WAP PUSH app. This property was used for selecting the APN in use in the APN list shown to the user. It was a bug and we fixed it by adding this property.