NEW ISSUE: binding decl for producer/consumer are problematic

Title: binding decl for producer/consumer are problematic

Target: assembly 1.2

Description:
The current WD of 1.2 allows for bindings to occur on producers, 
consumers and channels. 1.2 eventing is a closed system, in the sense 
that Producers and consumers are allowed to connect only to one or more 
channels in the SCA domain. This scenario is therefore very analogous to 
an SCA reference where the reference is not wired to an external 
service. In that case, we disallow references from having a binding. 
Instead we require the the target of the reference use 
<service-name>/<binding-name> to select a binding offered by the service.

The eventing analog of this is channels offering zero or more bindings 
and the Producer/Consumer source/target can be connected to 
<channel-name>/<binding-name>

Proposal:
Outline -- remove the producer/binding and consumer/binding elements and 
allow target/source to point to <channel-name>/<binding-name>

-Anish
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