Implement long-term condition subscriptions.

Bind long-term conditions (like "in a meeting") to enter/exit
zen mode automatically.

Persist automatic condition subscriptions to maintain them across
reboots.

Normalize condition state binding: true => enter zen, false => exit.

Change-Id: Icba2b8b25c0a352ae8215f4c0a324e4f966c0165
7 files changed