Encrypt files

Basic encryption/decryption.

**Encryption**
* File is copied to an encrypted version of itself
* File name is postfixed with `.CRYPT` to recognize them for now. This is easy to change.

**Decryption**
* File is copied to original version of itself
* File name's postfix `.CRYPT` is removed
* Some `NativeGCMCipherException` is thrown in the depths of the crypto library, I cannot find why and what it means. I can, however, catch it, log it, ignore it :)