Re-write of channel management

[pardahlman]

The ChannelFactory of today is a 300+ lines implementation that hold a channel pool and takes recovery of channels and connection into consideration, has dynamic pool scaling capabilities etc. Here's the vision for this re-write:

• Smaller classes, single responsibility design. Separate pooling capabilities to specialized classes. The "scale up" and "scale down" functionality should be contained in a more specialized class etc.
• No more ConnectToBroker() calls from the constructor. This ties in the discussion in Polly Policies not Executing #268 (comment).
• Implement and register a channel factory in the Polly enricher's plugin.
• Use dedicated channel pools for certain operations. At this point, the Publish action needs it's own channel pool in order to mitigate PublishConfirmException when doing RPC before publishing a message. #274