File en-/decryption with Streams

This adds en-/decryption which can handle big files by using Streams.
Additionally a test file is added to test this function (only ~100 Bytes).
#150 is closed by this.
First #146 and #161 have to be merged, then I need to rebase^^
SYMM_NONCE_SIZE_BIT / 8 is used so often all over the code that it might be better to introduce an own static final int SYMM_NONCE_SIZE_BYTE