FixedEncryptorSource takes hardcoded key id and content key. Implemented an AES Encryptor using OpenSSL. Change-Id: I59ba9a41fc0f40925d697045dd1b147b7351c2f9
Also includes a dummy packager_test with TestingMuxer. Change-Id: I6a6e6dd77e343ef742adc1846ede203993628943