Update message flow for shim-layer architecture

Update message flow for shim-layer architecture

This patch is updating the message flow for "capacity management",
"reservation management", and "allocation management" for the shim-layer
architecture.
It also starts a new (but still empty) section on the shim-layers
internal logic and operations. This section will be updated with a
separate patch.

JIRA: PROMISE-63

Change-Id: I131a5c34c7e145153831556321e7366af0401c8c