Event routing behavior

[jlabedo]

Why is this change proposed?

• Synchronous and asynchronous event handler priorities have the same behavior. Previous bahavior:

For synchronous we order endpoints in publish subscribe channels by priority. But a publish/subscribe channel is very thin: one per exact listenTo,
For asynchronous we add a 'priority' header. Message are polled from queue by priority header

• B/C: Respect ordering of event handlers routed by name or by object (current behavior is first object routing then named routing)
• decoupling between modules
• Reuse routing logic in other components (see following PR for PDO event sourcing: Event routing for pdo event sourcing jlabedo/ecotone-dev#4)
• Fixes Scheduling the same command multiple times for multiple handlers #465

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