Rebase test suite to be more modular
Simple mockup for publish/subscribe signal model
Add a check (predicate) callable to the signal connect

This allows another signal condition to the connection, so that, in addition
to the (sub) class, another check can be made before the signal is delivered
to the connected callable
Merge pull request #577 from greezybacon/feature/signals

Implement a simple signal (event) architecture

Reviewed-With: Peter Rotich <peter@osticket.com>