Implemented drive status support in drive register structure and code.

Added drive status reporting in scheduler
Added drive status reporting in OStoreDB
Added support for drive status listing in the front end
Removed virtual functions from the Scheduler, which is never overloaded.
Added DesiredDriveState structure to drive state.
Removed usage of duplicate MountType, DriveStatus and DriveState structures.
Created DriveInfo structure to allow recreation of drive register entry in all
reporting situation (potentially with partial/assumed info).