Remove HasFlowId and improve propagation logic

[bitzl]

Problem
To trace a processing flow to a workflow graph one has to enable tracing via FlowBuilder.propagateFlowIds(true) and either use FlowMessage or implement the interface ?HasFlowId. This is complicated, as the information if tracing is desired is distributed (flag and interface). There are also multiple ways to use tracing in a message class (use FlowMessageorHasFlowId) with the less recommended approach beeing the most visible one (using FlowMessagemeans for most people just to useDefaultMessage`).

Solution
For tracing

• check if incoming and outgoing messages implement TraceableMessage
• check if incoming message has a value for flow id and set that for the outgoing message

Remove old tracing mechanisms:

• remove FlowMessage as suggested in Replace FlowMessage by TraceableMessage #147
• remove HasFlowId
• remove the tracing flag from FlowBuilder, Flow and Job

Questions
Can we have sanity checks if both incoming and outgoing message types are traceable messages on application start?