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^^
I'd also strictly hard-code that Nonce-Byte-Size - having these /8 divisions appearing so many times is bug-attracting, incomprehensible and (probably) inefficient because JVM keeps calculating this 3-shift again and again. Please  fix this!