Stagger process starts

[jbbarth]

Somehow related to #108, low urgency: when starting a simpleflow process (Worker, Decider) we start everything at once. Here at Botify we usually have 8 subprocesses for each master process, and we have many activity workers (sometimes > 50), each having multiple master processes. Numbers add up quickly, so maybe we should stagger process start inside a given master process (say, start only one child process each second).

Low priority, just a thought for later.