FR-17: Show list of temporarily decrypted files

[skarpushin]

Idea is that if file was decrypted it was decrypted temporarily. Which means it has to be encrypted back and decrypted version have to be deleted! Program should keep track of all decrypted files and show them in table allowing user to manage decrypted content and easily encrypt it back and perform other useful operations.

HTD:

• Decrypt some files
• Expect: All decrypted files will appear in the decryption history table (in the main window) in chronological order
• Expect: row will automatically disappear from this table if decrypted file will disappear from disk
• Expect: Columns: Encrypted location | Decrypted location
• Expect: If encrypted version doesn't exists then "Encrypted location" field will be preceded with "DELETED:" prefix to make sure user notices that encrypted version is no longer exists
• Expect: Program will keep track of these files even after restart

Not sure -- do we need it? I doubt user will want to have too many un-encrypted files at the same time. And for the few files following features seem redundant:

• Expect: Filter by name
• Expect: Filter by decryption status (show only those which decryption product is still decrypted)

Postpone (will be impl as a part of other feature):

• There is a button "Encrypt all back and cleanup" (which means "Encrypt all files back and delete non-encrypted versions")
• Expect: program will silently encrypt all files back but only for those files that don't have any problems. In case of problems application will report causes to user.