Bug 828654 - pre: make BagheeraRequestDelegate callbacks include namespace and id.

This is convenient for my use of the Bagheera client, and prepares us
for having the server generate ids.
Bug 828654 - Part 1: Implement HealthReportUploadPolicy.
Bug 828654 - Part 2: Implement AndroidHealthReportUploadClient.
Bug 840127 - Delete obsolete documents when health report uploading is turned off.