Complete session hadling refactoring

All parts of system have been refactored. Session creation has been
simplified. Now session is created only when it is desperately needed and
its using is maximized instead of uncontrollable producing for each and
every block of code which is supposed to communicate with db.

This refactoring simplifies db data transfer management and makes it
more explicit for further developing.

Unit and functional tests have been updated.

Change-Id: I15a980432f9da5cac5f04b1f4f4af64d1a002b60
Pecan TransactionHook was added

All actions that were implemented on ExceptionHandlingHook and
SessionHook were moved to CustomTransanctionalHook which introduces more
flexible way to manage db communications while request processing via
pecan.

Change-Id: I8ab20b4be30d307b3c25fff27dc774209c8522ad
Merge "Complete session hadling refactoring"
Merge "Pecan TransactionHook was added"