Update DownloadRequest API

- Add set/getOpaqueData methods so middleware has one thing to persist
- remove id from DownloadRequest since nobody seems to want it
- replace FileServiceInfo with a service ID
- add a FileInfo extra when sending file-completion to the app

Change-Id: I75be3cce923d5d3c74081d344074b4e3c67deff3
4 files changed