Support for notifying specific observers using observation Id

Support for notifying specific observers using observation Id

1. Initial code changes
2. Combine GET & observe registration calls to entity handler into a single call; support for CON messages in NotifySpecificObservers; updates sample server app
3. Added the support for immediate observe cancelation in OCCancel
4. Fixed the new interface to OCCancel in C++ layer
5. A temp solution for the case when observation sequence number wraps around.
6. Merging with Yamin's changes
7. Changed OCNotifyObservers to OCNotifyAllObservers
8. Build issue
9. Another Merge to support calling the entity handler when deregister an observer
10. Rebase & CPP Changes from Sudarshan and Sashi to support Notify specific observers.
11. Command line argument options for simpleserver (so it can choose between all observers or specific observers)
12. CPP bugfix.
13. Fixed review comments for CPP.
14. Changed COAP_DEFAULT_RESPONSE_TIMEOUT to 2 and all the sample applications to sleep accordingly.
15. Fixed review comment for new line.
16. Fixed review commend for line exceed.
17. Response to comments received on patch 11
18. Header file comments updated

Change-Id: I03aa7ab2a580899441b70bd2a76cca05575b192a