Refactoring: make NSMountLogic class responsible for Channel and MntMonitor

Refactoring: make NSMountLogic class responsible for Channel and MntMonitor

NSMountLogic class will now be solely responsible for making updates to
mount namespaces of running applications. It's single instance will be
persistent in ServiceImpl class. NSMountLogic now owns Channel for
communicating with the Worker process and sends requests for mount updates.
It also listens to mount events from MntMonitor and sends appropriate
requests to worker.

All required synchronization should be done in NSMountLogic.
NSMountLogic::check() method needs to be thread-safe because it may be
called concurrently from ServiceImpl and from MntMonitor thread.

Change-Id: I8cb4be25e5f9c8da4360d7ddff34993836f9f169
Signed-off-by: Rafal Krypa <r.krypa@samsung.com>