Implement virtual tape library for emulated tape volumes.

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From Tim Sirianni:
2)  Also, has anyone suggested to do the same thing you're talking about with 
disks [support multiple indexedDB databases for separate disk subsystems and 
and system configurations] except for tapes? Set up a sort of a virtual tape 
library. The tape drives could be directly unloaded into the IDB-backed 
library, indexed by the VSN. As soon as you hit UNLOAD, the data on the tape 
just goes to the library. Later we could type a VSN into a UI that pops up when 
a tape drive's LOAD is pressed and have that tape load. Tapes could be exported 
from and imported to the library in the same way the tape drives currently 
handle it. Also fun would be if tape drives could be restored to a saved state 
(including online/offline, write-protect, and "which VSN/scratch tape is 
loaded?" status) at power on time.

Original issue reported on code.google.com by paul.kimpel@digm.com on 20 Jul 2014 at 2:45