Bug 1097220 - Part 1: extend ClientRecord and add fields to new local client records.
Bug 1097220 - Part 2: extend ClientsDatabase to support new optional fields.
Bug 1097220 - Part 3: extend TestClientsStage to cover new fields.
Bug 1097220 - Part 4: test that optional fields are initialized to null.
Review comment: note that HardwareUtils is safe to init multiple times.
Review comment: rename optStringFromCursor, add comments.
Review comment: add pointer to docs and note about optional fields.
Bug 1097220 - Extend client record format for Android. r=nalexander