Add signals to AppArmorProfile spec

[Edan-Hamilton]

What would you like to be added:

Add the ability to restrict signals with AppArmorProfiles. Should include read, write, send, or receive. Should be able to apply to specific signals, or all signals. Should be able to limit to a specific peer.

Why is this needed:

Signals allow communication between processes, which is an inherent security risk. Certain signals are commonly required, but most are not. Often a profile can be further restricted by allowing signals only to itself, or only to other processes with a specific profile.