Deprecating the Schma-dependent Plugin CRUD APIs and Introducing Schema-independent CRUD API definitions in the Plugin layer.

1. Deprecated all the existing insert/get/update/Delete methods that are Open_vSwitch Schema-dependent
2. Introduced equivalent methods with DatabaseName as an additional argument.
3. Introduced a new inssertTree method that has the capability to insert a Tree of rows with parent-child relationship
4. Changed the return types to make more sense (instead of the status types returned today)
5. Added a more generic Exception class which will be inherited by more specific exceptions as the need araises.

The implementation for these methods are not done yet.

Change-Id: Ia363574a4d71e301f7c4b1a2e3bac08de53c62f9
Signed-off-by: Madhu Venugopal <mavenugo@gmail.com>