Added aes-128-cbc encryption in plugin using pycrypto.
Save encryption details to kek_metadata, not datum.mime_type.
Secret can have more than one encrypted datum.
Only use byte type in plugin.
Merge upstream changes.
Merge pull request #72 from dmend/master

Added aes-128-cbc encryption in sample plugin using pycrypto
Added better error feedback to clients; Added missing unit tests;