Message Subscribe and Unsubscribe: body spec change

[pchainho]

Currently, addresses to be subscribed or unsubscribed from MN are defined with "subscribe" and "unsubscribe" fields, respectively.

To make it more consistent, we would like to propose to use the field "resources", for these messages.

Since, this would impact the MN implementations, @sdruesedow , @jboulmal , @avallee-apizee what do you think?

For the same reason, we would like also to always use the field "source" to identify the original sender of the message in case the "from" is not. This would mean to use "source" instead of "subscriber" for subscription messages exchanged between Sync Managers

This change would only impact the Runtime sync manager implementation

[sdruesedow]

The required changes on the MN side seem marginal and will simplify some code. It will also implicitely fix the problem with wrong "unsubscribe" messages. I support it.

[jboulmal]

It's fine