Bug 1764 - moved Session related interfaces to openflowplugin-api

- session related interfaces moved from implementation to api
- Extension related methods erradicated from SessionManager and
  moved to extension-api's ExtensionSessionManager
- openflowplugin-api SessionManager and openflowplugin-extension-api ExtensionSessionManager
  joined for openflowplugin neeeds in ConjuctSessionManager to provide functionality
  of both apis

(cherry picked from commit 27aed9a50ceeffc36468ff9610d6183c3aed14df)
Change-Id: I947a59714900cb7e6d2fb7376c4d743e1764ac7b
Signed-off-by: Martin Bobak <mbobak@cisco.com>
Signed-off-by: Michal Rehak <mirehak@cisco.com>
Bug 1764 - implementation of default config pusher

(cherry picked from commit e94d9d2778478e996451ec25044aa229a2e3f8e2)
Change-Id: I6f910c3b68f6e50fb3de2e12b01fc33bb28eb80c
Signed-off-by: Martin Bobak <mbobak@cisco.com>
Signed-off-by: Michal Rehak <mirehak@cisco.com>