General code cleanup as reported by the PHPStorm static code
analysis. I hope it's not a problem that I made a lot of very
different (but all very tiny) changes in a single patch. If you
want to merge this but you think it's better to split it into
several patches first, please tell me.
Change-Id: I2e2c4bb47f8d20e038d28e236e2ff813b30504af
Implements whitelists and blacklists for notification agents to assist
in filtering out unwanted notifications from bots.
Bug: 47946
Change-Id: I0d7e071067c6974fb90cf6c0ba1bd159f46bd5df
