Client requests to delete a resource.

Client requests to delete a resource.
*Patch 1:
  1. Process request at C apps' level.
  2. Move logic into the C stack instead of app level.
  3. C stack responds to request to a 'to be deleted' resource.
*Patch 2: Added fixes per Sachin's code review.
*Patch 3: Added improvements per Jesse's code review.
***Abandoned changeset #293
***Restarted with changeset #304
*Patch 1: Rebased and changed Makefile per Jesse's feedback.
*Patch 2: Removed 'mark to be deleted' logic per design changes
          and added checks for entity handler result code.
*Patch 3: Fixed build error due to missing newly added coap code.
*Patch 4: Added improvements per Joey's feedbacks.
*Patch 5: Removed extra semicolon in enum to avoid build error.
*Patch 6: Rebased from Joey's changeset #313 and applied my changes on top.
*Patch 7: Rebased of master which has Joey's changeset #313, and added my changes on top.
*Patch 8: Added improvements per comments from Joey and Vijay

Change-Id: Iacec6f56c9f7ce7f61bfda8a47e84368edaf822e