add BASE 64 DK support , add one line keyfile support

[forrest96]

Hi there,
so far I had no issues on testing the encryption with ltfs.
But the program need some improvements to be useful.

1. Any cartridges should be associated to one DKi
   (is the DKi usually written to the cartridge ?)
2. Support for BASE64 encoded string of 256-bit data as DK
3. The Keyfile should have one or more lines of DKi and DK :
   BASE64 encoded DK : Alias of Data Key

On this website you can see how IBM managed the DK and DKi setup.
https://www.ibm.com/support/knowledgecenter/en/STQNYL_2.2.2/ltfs_sde_gui_data_key_config_win.html

Kind regards

my configuration :
Quantum Ultrum 5 Cartridges (with ltfs partition)
Tandberg LTO-5 HH (Firmware Z629/OEM)
HP SmartArray P410
ltfs driver from HP (IBM driver do not recognize the device)