Reviewer Ellie - Various Application ID fixes

This fixes both https://github.com/Metaswitch/ralf/issues/78 and https://github.com/Metaswitch/ralf/issues/77.

Make sure we report Rf billing as an Accounting Application rather than an Authorization Application and make sure we include the application ID in ACRs we send.

Please don't merge as I need to update `cpp-common`.